This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
| Lines | Role |
|---|---|
| 0, 2 | Raw Z80 machine code stored in REM operand bytes |
| 3–6 | Human-readable metadata REMs (compiler name, copyright) |
| 9 | SAVE the machine code to tape |
| 10 | POKE to patch system workspace |
| 20 | Invoke compiler via USR 18821 |
| 25 | SLOW mode for stable display |
| 30–80 | Title screen output |
| 90, 110 | Delay subroutine calls |
| 100 | Post-install instruction message |
| 120 | STOP |
| 200–230 | Delay loop subroutine (FOR/NEXT + CLS) |
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx(CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture. ED 52(SBC HL,DE) used in arithmetic comparisons throughout.ED B0(LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40= 16396,1C 40= 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821is assigned toLat line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic. - The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25). - Line 9 saves the program to tape as
MCODEbefore the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM \BF\BD\AC\B9\C3\B4\C3\C3\C3F\C3\C3\C3\AB\C3\C3C\C3\DE\C3\C3A\C3\C3\B8\CFC\E5\D5\AF\CD\CBCE\CD\CD itemtype='https://schema.org/Blog' itemscope='itemscope' class="wp-singular computer_media-template-default single single-computer_media postid-56696 wp-custom-logo wp-embed-responsive wp-theme-astra wp-child-theme-astra-child ast-desktop ast-separate-container ast-left-sidebar astra-4.12.6 group-blog ast-blog-single-style-1 ast-custom-post-type ast-single-post ast-inherit-site-logo-transparent ast-hfb-header ast-full-width-primary-header ast-box-layout ast-normal-title-enabled astra-addon-4.12.4"B\CD itemtype='https://schema.org/Blog' itemscope='itemscope' class="wp-singular computer_media-template-default single single-computer_media postid-56696 wp-custom-logo wp-embed-responsive wp-theme-astra wp-child-theme-astra-child ast-desktop ast-separate-container ast-left-sidebar astra-4.12.6 group-blog ast-blog-single-style-1 ast-custom-post-type ast-single-post ast-inherit-site-logo-transparent ast-hfb-header ast-full-width-primary-header ast-box-layout ast-normal-title-enabled astra-addon-4.12.4"A\E8\CD
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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D\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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D\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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D\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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A\CD\AB\CD\AE\E1\CD\AEE\ED\CDBEB\CD\ABE\A7\ED\CD\ABE\FA\E1\CD
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
Image Gallery
Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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E\CD\A9\EB\D1\C3\AE\C3\C3B\C3E\C3\C3\C3\C3A\C3D\C3\A0\EB\C3\A3\C3\A6\C3\A9\C3\AC\C3\AF\AF
2 REM D\E5EEE\D1\A7\ED\EB
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\C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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM \BF\BD\AC\B9\76\76\C3\B4\40\C3\23\41\C3\57\41\C3\4F\41\C3\85\41\C3\97\41\C3\AB\41\C3\21\42\C3\9C\42\C3\DE\42\C3\39\43\C3\7A\43\C3\57\43\C3\B8\43\CF\8C\E5\D5\AF\CD\21\42\CB\7C\28\08\3E\16\CD\21\42\CD\1B\41\11\10\27\CD\07\41\30\1A\11\E8\03\CD\07\41\30\15\11\64\00\CD\07\41\30\13\1E\0A\CD\07\41\30\12\C3\FC\40\CD\0D\41\11\E8\03\CD\0D\41\11\64\00\CD\0D\41\1E\0A\CD\0D\41\1E\01\CD\0D\41\AF\D1\E1\C3\21\42\E5\A7\ED\52\E1\C9\3E\1C\A7\ED\52\38\03\3C\18\F9\19\C3\21\42\7C\2F\67\7D\2F\6F\23\C9\2A\0C\40\11\21\00\E5\01\00\00\09\23\E5\19\EB\21\D6\02\ED\42\E3\C1\EB\ED\B0\E1\01\B6\02\09\22\0E\40\3E\21\32\39\40\3E\03\32\3A\40\C9\CD\BB\02\7C\FE\FE\20\0E\CD\BB\02\24\20\FA\CD\BB\02\7D\FE\FF\28\F8\01\7F\FD\AF\E5\ED\42\E1\CA\B2\40\01\EF\FC\AF\E5\ED\42\E1\28\DD\44\24\C8\4D\CD\BD\07\7E\FE\00\C9\CB\FC\22\34\40\2A\34\40\7C\E6\7F\B5\C8\CD\4F\41\28\F3\06\10\4A\7B\EB\21\00\00\CB\39\1F\30\01\19\EB\29\EB\10\F5\C9\3E\2B\90\DA\DC\42\47\3E\01\CB\28\30\02\3E\04\CB\29\30\02\CB\07\F5\CD\EB\41\7E\CB\07\FE\10\30\07\CB\0F\30\02\EE\8F\47\11\9E\0C\3A\30\40\93\FA\E1\41\F1\2F\A0\18\02\F1\B0\FE\08\38\02\EE\8F\18\36\3E\17\90\DA\DC\42\79\E6\1F\4F\C5\C5\C5\AF\CB\10\CB\10\CB\10\68\67\29\29\C1\48\47\09\C1\47\09\ED\4B\0C\40\09\23\22\0E\40\C1\3E\18\90\32\3A\40\3E\21\91\32\39\40\C9\D5\E5\C5\F5\3A\3A\40\FE\02\28\3A\F1\FE\76\28\2A\FE\40\30\72\2A\0E\40\77\23\22\0E\40\3A\39\40\3D\32\39\40\7E\FE\76\20\4A\3A\3A\40\3D\32\3A\40\23\22\0E\40\3E\21\32\39\40\18\38\2A\0E\40\7E\FE\76\28\E6\23\18\F8\2A\0C\40\01\F8\02\09\36\8F\CD\4F\41\28\FB\FE\28\28\15\FE\3F\28\1B\FE\29\20\08\21\10\27\2B\7D\B4\20\FB\CD\23\41\18\03\CD\2A\0A\F1\18\9A\C1\E1\D1\C9\CD\69\08\18\D3\78\B1\C8\1A\CD\21\42\13\0B\18\F5\FE\43\38\09\FE\C0\CB\B7\DA\35\42\E6\3F\21\11\01\47\04\FE\21\30\04\AF\CD\21\42\CB\7E\23\28\FB\10\F9\7E\CB\7F\20\06\CD\21\42\23\18\F5\E6\3F\CD\21\42\AF\C3\2D\42\CF\8A\7B\B2\28\FA\CD\29\43\C5\7C\B2\07\38\F1\4B\42\11\00\00\D5\EB\23\29\EB\29\79\95\78\9C\EB\30\F6\EB\EB\AF\7C\1F\67\7D\1F\6F\B4\28\18\EB\AF\CB\1C\CB\1D\79\95\78\9C\FA\FE\42\79\95\4F\78\9C\47\E3\19\E3\18\DD\E1\C1\CB\78\C2\1B\41\C9\44\7C\17\DC\1B\41\EB\7C\A8\47\CB\7C\C2\1B\41\C9\ED\5B\32\40\63\2E\FD\7A\B7\06\00\ED\52\98\ED\52\98\5F\50\ED\52\30\01\23\22\32\40\CB\BC\C9\03\03\03\C5\03\03\03\03\21\80\49\CD\A3\09\23\3E\76\71\23\36\02\23\C1\71\23\70\23\36\EA\23\77\23\77\23\C9\21\00\00\E5\E5\CD\57\41\FE\16\20\09\E1\D1\F5\E5\CD\21\42\18\F0\FE\76\E1\28\1F\29\E5\29\29\D1\19\4F\CD\21\42\79\D6\1C\38\08\4F\06\00\09\FE\0A\38\D3\F1\3E\E6\CD\21\42\18\C7\F1\CC\1B\41\C9\C5\E5\2A\7B\40\F5\77\E5\23\22\7B\40\CD\4F\41\FE\29\20\12\3E\76\CD\21\42\E1\CD\B4\40\F1\26\00\6F\CD\B4\40\18\02\E1\F1\E1\C1\AF\C9\C9\C9\3E\0F\D7\CD\75\49\18\12\21\00\00\CD\12\44\CD\F7\48\03\CD\78\49\E5\CD\06\49\E1\CD\12\44\CD\59\49\CD\20\44\CD\0D\44\CF\7F\3E\C9\C3\7B\49\22\70\40\ED\5B\1C\40\13\21\72\40\CD\09\45\2A\70\40\36\18\23\36\68\23\22\79\40\11\68\00\19\22\7B\40\21\7D\40\CD\D4\44\23\23\E5\23\22\16\40\CD\44\45\FE\F2\CC\CB\44\FE\F9\CC\96\48\FE\FA\CC\C8\48\FE\DE\28\EA\FE\E9\CC\1D\49\FE\EC\CC\2B\45\FE\ED\CC\40\45\FE\EB\CC\C7\47\FE\F3\CC\F4\47\FE\E4\CC\00\49\FE\F4\CC\B6\47\FE\E5\CC\F1\48\FE\EE\CC\5D\48\FE\F6\CC\6C\48\FE\FC\CC\92\48\FE\F1\CC\03\46\FE\FB\CC\9F\47\FE\E3\CA\96\47\FE\F5\CC\55\45\FE\EA\28\15\FE\E7\CC\A4\47\FE\FE\CC\0D\44\FE\00\20\0E\CD\44\45\FE\76\20\07\E1\CD\0E\49\C2\36\44\3E\B8\CD\68\49\CD\59\49\CF\9B\CD\4D\47\21\5F\49\C3\A9\47\E5\56\23\5E\D5\EB\E5\22\23\40\22\0A\40\CD\EC\45\CD\53\49\E1\CD\13\45\1B\1B\EB\D1\CD\09\45\ED\5B\7B\40\CD\09\45\E5\ED\5B\72\40\A7\ED\52\E1\38\03\22\72\40\E1\C9\73\23\72\23\C9\5E\23\56\23\C9\E5\C1\2A\1C\40\23\CD\0E\45\EB\A7\ED\42\D0\2A\72\40\ED\52\D8\EB\23\18\ED\3E\C3\F5\CD\44\45\CD\2A\48\CD\13\45\EB\CD\0E\45\EB\F1\C3\AB\47\3E\CD\18\E9\E5\E7\FE\76\28\09\FE\7E\28\05\F5\CD\68\49\F1\E1\C9\CD\44\45\FE\76\28\77\FE\0B\28\13\FE\C1\28\4C\FE\D6\28\74\CD\50\47\21\53\49\CD\A9\47\18\4F\3E\18\CD\7B\49\2A\7B\40\E5\CD\7B\49\01\FF\FF\2A\16\40\23\03\7E\F5\CD\68\49\F1\FE\0B\28\05\CD\7B\49\18\EF\22\16\40\E1\C5\71\23\3E\11\CD\AB\47\3E\01\E1\CD\AB\47\21\6B\49\CD\A9\47\18\12\CD\37\47\CD\C1\47\21\43\4D\CD\AE\47\21\F5\08\CD\A9\47\CD\44\45\FE\1A\28\8C\FE\19\28\88\21\EC\45\CD\A9\47\2A\16\40\2B\22\16\40\AF\C9\CD\4D\47\3E\7D\CD\7B\49\21\68\49\CD\A9\47\18\D6\3E\76\C3\68\49\FE\40\D2\C1\44\D6\26\17\17\ED\4B\79\40\26\00\6F\09\C9\CD\44\45\CD\F1\45\FE\64\20\0A\CD\2A\49\3E\E5\CD\7B\49\26\FF\E5\CD\44\45\FE\14\C2\C1\44\CD\3D\46\CD\D3\45\E1\7C\FE\FF\20\0C\21\D1\EB\CD\AE\47\21\09\45\C3\A9\47\3E\22\C3\AB\47\AF\F5\CD\4D\47\3E\E5\CD\7B\49\CD\44\45\FE\11\28\50\FE\76\28\4C\F5\CD\4D\47\F1\FE\15\28\04\FE\16\20\23\C1\67\78\FE\00\20\04\F5\E5\18\D8\E5\21\44\4D\CD\AE\47\CD\7E\46\3E\E5\21\69\60\CD\AB\47\18\C4\F5\C5\18\1C\FE\18\28\10\FE\17\C2\C1\44\CD\C6\46\21\62\49\CD\A9\47\18\AC\CD\C6\46\21\6E\49\18\F3\3E\E1\CD\7B\49\F1\FE\00\C8\FE\15\28\11\CD\C6\46\21\A7\EB\CD\AE\47\21\ED\52\CD\AE\47\18\E7\CD\C6\46\3E\19\CD\7B\49\18\DD\3E\D1\C3\7B\49\FE\D3\20\0F\CD\4D\47\21\7E\6F\CD\AE\47\21\26\00\C3\AE\47\FE\D4\20\12\CD\4D\47\21\EB\46\C3\A9\47\01\F1\46\C5\E5\C9\44\4D\C9\FE\C4\C2\0F\47\CD\44\45\FE\41\C2\C1\44\21\5C\49\CD\A9\47\3E\26\21\00\6F\C3\AB\47\FE\40\C2\1A\47\21\72\49\C3\A9\47\FE\D2\20\11\CD\4D\47\21\CB\7C\CD\AE\47\3E\C4\21\7A\47\C3\AB\47\FE\CF\C2\C1\44\C3\4D\47\CD\4D\47\CD\44\45\F5\3E\E5\CD\7B\49\CD\4D\47\3E\D1\CD\7B\49\F1\C9\CD\44\45\FE\16\F5\CC\44\45\FE\10\28\16\FE\40\30\0D\FE\26\D4\82\47\DC\8F\47\F1\CC\75\47\C9\CD\CB\46\18\F6\CD\3D\46\18\F1\21\7A\47\18\2F\7C\2F\67\7D\2F\6F\23\C9\CD\F1\45\FE\64\CA\3F\49\3E\2A\C3\AB\47\CD\2A\48\3E\21\18\15\CD\0D\44\E1\ED\4B\7B\40\C9\21\2A\0A\18\05\21\56\49\18\00\3E\CD\CD\7B\49\7D\CD\7B\49\7C\C3\7B\49\CD\37\47\CD\C1\47\21\EB\73\18\ED\FE\1A\C2\C1\44\C9\CD\44\45\CD\F1\45\E5\E5\CD\44\45\CD\37\47\3E\23\CD\7B\49\21\ED\53\CD\AE\47\E1\CD\AE\47\3E\22\23\23\CD\AB\47\E1\ED\5B\7B\40\CD\09\45\C9\CD\44\45\CD\F1\45\E5\E5\3E\2A\CD\AB\47\21\23\22\CD\AE\47\E1\CD\AE\47\23\23\3E\ED\CD\7B\49\3E\5B\CD\AB\47\3E\A7\21\ED\52\CD\AB\47\3E\FA\E1\CD\0E\45\EB\CD\AB\47\C9\21\00\00\18\0F\CD\44\45\FE\7E\28\1A\F5\11\0A\00\CD\62\49\F1\FE\26\D2\C1\44\FE\1C\DA\C1\44\D6\1C\06\00\4F\09\18\DF\E5\2A\16\40\11\05\00\19\22\16\40\E1\C9\21\75\49\CD\A9\47\CD\44\45\CD\F1\45\C3\38\46\3E\9B\F5\CD\37\47\CD\C1\47\21\4B\45\CD\AE\47\3E\3E\CD\7B\49\F1\CD\7B\49\3E\32\21\30\40\CD\AB\47\21\65\49\C3\A9\47\3E\A0\18\D8\3E\2A\21\34\40\CD\AB\47\3E\22\21\32\40\C3\AB\47\FE\DD\28\12\FE\14\28\14\1F\30\01\EB\17\A7\ED\52\37\F8\17\D0\18\08\ED\52\37\C0\18\04\ED\52\37\C8\3F\C9\CD\37\47\67\2E\3E\CD\AE\47\21\A6\48\CD\A9\47\2A\0A\40\23\CD\13\45\EB\CD\0E\45\EB\3E\D2\CD\AB\47\CD\44\45\FE\DE\C2\C1\44\C9\21\F7\48\C3\A9\47\CD\E7\02\21\3B\40\CB\B6\C9\21\06\49\C3\A9\47\21\3B\40\CB\F6\C3\07\02\4E\23\46\09\23\3A\0C\40\9D\C0\3A\0D\40\9C\C9\CD\44\45\FE\3F\C2\C1\44\CD\4D\47\AF\C9\CD\4D\47\21\ED\4B\CD\AE\47\21\1C\40\CD\AE\47\21\29\09\C3\AE\47\CD\2A\49\3E\D5\CD\7B\49\21\0E\45\CD\A9\47\21\EB\D1\C3\AE\47\C3\88\40\C3\8B\40\C3\8E\40\C3\91\40\C3\94\40\C3\97\40\C3\9A\40\C3\9D\40\C3\A0\40\EB\C3\A3\40\C3\A6\40\C3\A9\40\C3\AC\40\C3\AF\40\AF\40
2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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MCoder
This program is a loader for “MCODER,” a ZX81/TS1000 BASIC-to-machine-code compiler. The bulk of the program is stored as raw Z80 machine code embedded in REM statements at lines 0 and 2, with the compiler entry point at address 18821 (USR 18821). Line 10 uses POKE 16389,118 to place a HALT opcode at a system address, a common technique for controlling program flow or patching the system workspace. After invoking the compiler via USR, the loader displays a title screen and instructs the user to delete all lines except 1–4, leaving only the machine code REMs resident in memory. A simple software delay loop using FOR/NEXT replaces a proper PAUSE call, giving a timed display before clearing the screen.
Program Analysis
Program Structure
The program divides into three logical parts: machine code storage in REM statements (lines 0 and 2), a system initialisation and title display section (lines 10–90), and a post-install instruction screen (lines 100–120), supported by a simple delay subroutine at lines 200–230.
Lines Role 0, 2 Raw Z80 machine code stored in REM operand bytes 3–6 Human-readable metadata REMs (compiler name, copyright) 9 SAVE the machine code to tape 10 POKE to patch system workspace 20 Invoke compiler via USR 18821 25 SLOW mode for stable display 30–80 Title screen output 90, 110 Delay subroutine calls 100 Post-install instruction message 120 STOP 200–230 Delay loop subroutine (FOR/NEXT + CLS)
Machine Code in REM Statements
Lines 0 and 2 contain dense Z80 binary data encoded as the operand bytes of REM statements. This is the standard technique for embedding machine code in ZX81/TS1000 BASIC: the interpreter skips REM content entirely, but the bytes sit at fixed, calculable addresses in RAM. Line 0 begins at the very start of the BASIC program area, placing the first byte of machine code at a well-known address. The REM at line 2 continues the binary image.
REM line 3 records the compiler name and two key addresses: ZXGT=17389 and PROG=18823, suggesting the compiled machine code image spans from address 17389 onwards, with the BASIC program starting at 18823.
System Initialisation Techniques
Line 10 executes POKE 16389,118. Address 16389 is in the system variables region; decimal 118 is the opcode for Z80 HALT (also the ZX81 NEWLINE/end-of-line token 0x76). This is a known idiom for patching system behaviour or setting a trap, depending on context within the compiler’s own initialisation sequence.
Line 20 calls USR 18821, transferring control to the machine code at that address. The return value is stored in L but is not subsequently used; the call is made purely for its side effects (compiler installation).
Line 25 invokes SLOW mode after the USR call returns, ensuring the subsequent PRINT statements render correctly under the standard one-in-five interrupt display scheme.
Display and Delay Idioms
The title screen uses PRINT AT r,c; with inverse-video character sequences (e.g. %M%C%O%D%E%R) to render highlighted text for the product name “MCODER” and %C %O %M %P %U %T %E %R for “COMPUTER” with spaced inverse letters.
The delay subroutine at lines 200–230 uses a FOR F=1 TO 80 : NEXT F loop followed by CLS. This gives a short timed pause before clearing the screen, a practical substitute for PAUSE when precise timing is not critical.
Post-Install Instruction
Line 100 instructs the user to delete all BASIC lines except lines 1–4. This leaves only the two machine code REM lines (0 and 2) and the metadata REMs (3–6) in memory, forming a clean resident compiler image. The loader itself is designed to be discarded after installation.
Notable Z80 Routines (Selected)
Scanning the machine code bytes in line 0 reveals several structured subroutine clusters. Notable patterns include:
- Repeated
CD xx xx (CALL) sequences suggesting a dispatcher or token interpreter loop, consistent with a BASIC compiler’s keyword-handling architecture.
ED 52 (SBC HL,DE) used in arithmetic comparisons throughout.ED B0 (LDIR) block copy instructions, used for moving code or data segments during installation.CB-prefixed bit manipulation instructions indicating flag testing and bitfield operations typical of a tokeniser or expression evaluator.- Address constants matching system variable locations (e.g.
0C 40 = 16396, 1C 40 = 16412) confirming direct system variable access.
Authorship and Licensing
REM line 4 records COPYRIGHT 1982 PSS, identifying Professional Software Specialists of Coventry, England as the original authors. REM line 80 confirms the product is distributed by Intercomputer Inc under licence from PSS. The compiler is named MCODER (stylised as MCODER in inverse video), a product known to have been commercially released for the ZX81/TS1000 platform.
Anomalies and Observations
- The return value of
USR 18821 is assigned to L at line 20 but never used; this is harmless and may be a remnant of an earlier diagnostic.
- The delay loop bound of 80 iterations is quite short and gives only a brief display before
CLS; the effect depends on SLOW mode being active (confirmed by line 25).
- Line 9 saves the program to tape as
MCODE before the USR call at line 20, meaning a fresh tape copy is made each time the loader runs — useful for distribution but potentially unintentional in normal use.
Content
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Source Code
0 REM 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2 REM \21\7D\40\E5\22\79\40\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\23\23\4E\23\46\09\23\D1\A7\ED\52\22\77\40\EB\2A\04\40\73\23\72\23\EB\2A\79\40\ED\4B\77\40\ED\B0\AF\C9\CD\E7\02\21\3B\40\CB\B6\2E\7D\E5\2A\04\40\4E\23\46\E1\E5\C5\CD\A3\09\2A\04\40\23\23\C1\D1\ED\B0\AF\C9\7D\40\00\00\75\00\00\00\00
3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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3 REM TAN -ZXGT COMPILER - ZXGT=17389 PROG=18823
4 REM %M%C%O%D%E%R COPYRIGHT 1982 PSS
5 REM
6 REM
9 SAVE "MCODE%R"
10 POKE 16389,118
20 LET L=USR 18821
25 SLOW
30 PRINT AT 5,11;"INTER"
40 PRINT AT 7,6;"%C %O %M %P %U %T %E %R"
50 PRINT AT 9,10;"PRESENTS"
60 PRINT AT 11,11;"%M%C%O%D%E%R"
70 PRINT AT 15,3;"(C)1982 INTERCOMPUTER INC"
80 PRINT AT 16,1;"UNDER LICENCE FROM PSS,COVENTRY ENGLAND"
90 GOSUB 200
100 PRINT AT 5,5;"YOU MAY DELETE ALL LINES EXCEPT 1 TO 4 INCLUSIVE"
110 GOSUB 200
120 STOP
200 FOR F=1 TO 80
210 NEXT F
220 CLS
230 RETURN
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.