ZX81/TS1000 Tips

12. Here is a set of Machine code routines that uses a Floating Point Number as an address. It is a very useful set of routines, as it enables you to input strings with machine code. We actually use the BASIC interpreter by copying the BASIC commands into the Print buffer everytime we need an input and make the BASIC Interpreter run it, then return to the Machine Code. For example we will set RAMTOP at 29952 (7500h) and our entry point to input A$, at 30000 (7530h). The routines are:

Storage:

   7500 0000            Store: SPARE 3
(29952)    0000                SPARE 4
                                          4 Bytes

Commands:

       LINE    COUNT   INPUT  A   $    N/L
7504   0000    0400      EE   26  0D   76 ; Input A$
       LINE    COUNT    RAND USR  0  NUMBER
750C   0000    0A00      F9   D4  IC   7E;  RAND USR 751B
        ___751B_____     N/L   N/L
7514   8FEA  360000      76    76           (29979)
                                          23 Bytes

751B E1  RAND USR 0;          POP HL
     ED 7B 7B 40              LD SP, (SPARE 2); Restore SP
     2A 00 75                 LD HL, (SPARE 3);
     22 29 40                 LD(NXTLIN), HL  ;(Restore NXTLIN)
7526 2A 10 40                 LD HL, (VARS)   ;get A$
     23                       INC HL          ;skip over string name
     4E                       LD C,(HL)       ;Low count
     23                       INC HL
     46                       LD B, (HL)      ;Hi count
     23                       INC HL
     7E                       LD A, (HL)      ;1st byte of A$
     C9                       RET
                                          21 Bytes

Note: This routine returns with HL pointing to the 1st byte of A$, BC contains the count and A contains a copy of the 1st byte.

7530 ED 73 7B 40    INA$:     LD(SPARE 2), SP  ; SAVE SP
     2A 29 40                 LD HL,(NXTLIN)
     22 00 75                 LD (SPARE 3), HL ; SAVE (NXTLIN)
     CD 9A 14                 CALL 149A, CLEAR
     21 04 75                 LD HL, Commands
     11 3C 40                 LD DE, PR-BUFF
     01 17 00                 LD BC, 0017      ; 23 bytes
     ED B0                    LDIR             ; Copy up
     21 76 06                 LD HL, 0676      ; Next-line
     E5                       PUSH HL
     21 3C 40                 LD HL, 403C      ; PR-BUFF
     22 29 40                 LD(NXTLIN), HL
     C9                       RET
                                          35 Bytes
                                    83 BYTES TOTAL