Multi Tape

This program catalogs tape headers from both TS2068 and Spectrum cassettes, storing the results in three parallel arrays: a numeric array `c(400,4)` for data length, start address, auto-start line, and program/vars length; a string array `n$(400,13)` for tape names/sides; and a string array `t$(400,28)` for header type and program name. A 53-byte machine code routine is POKEd into RAM starting at address 64000 and called via `RANDOMIZE USR 64000` to read raw tape header bytes into memory around address 64060, which BASIC then inspects with `PEEK` to decode header fields. The catalog can hold up to 400 entries and supports searching by program name or tape name, listing all programs, displaying full header details, and saving the catalog back to tape. The program requires a `CLEAR 63999` before reloading for the “continue cataloging” option (option 4) to preserve the arrays already in memory.

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Program Analysis

Program Structure

The program is organized into distinct functional blocks accessed via a numbered menu at line 60. Lines 1–4 serve as a one-time instruction screen, after which line 5 sets a global error handler and line 9 jumps to the main menu at line 55. The menu at lines 60–98 polls INKEY$ in a tight loop and dispatches to subroutines for each option.

Lines	Function
1–4	First-run instructions (intended to be deleted)
10–40	Option 1: List all programs (brief format)
50	SAVE with auto-start at line 55
55–98	Main menu and dispatcher
100–140	Option 2: Search by program name
200–240	Option 3: List programs on a specific tape
300–340	Raw header dump (all fields)
400–440	Option 7: Show full header detail for one entry
500–540	Option 8: Show unique tape names (also a subroutine for option 3)
9850–9865	Option 4: Continue cataloging (with CLEAR 63999 check)
9870–9875	Shared machine code POKE and tape-name input for option 4
9970–9995	Option 5: Fresh catalog start; machine code load and header reading loop
9980–9982	DATA statements containing the 53-byte machine code routine

Machine Code Routine

The core of the cataloging mechanism is a 53-byte Z80 machine code routine POKEd into addresses 64000–64052 via a FOR/READ/POKE/NEXT loop at lines 9870 or 9970. It is invoked with RANDOMIZE USR 64000 at line 9982. This routine reads a tape header block and deposits the raw bytes into memory starting around address 64060, which BASIC then reads back using PEEK.

The DATA bytes span lines 9980–9982 (27 + 26 = 53 bytes, with the loop running 64000 TO 64052, giving 53 iterations). The first byte, 55 (decimal), disassembles as Z80 PUSH HL, and the routine references I/O port 244 (the cassette EAR port area) and port 255, consistent with tape reading on this hardware. The result byte at address 64060 encodes the header type (0=PROGRAM, 1=NUMERIC ARRAY, 2=CHARACTER ARRAY, 3=BYTES).

Data Storage Arrays

Three parallel arrays are dimensioned at line 9972 for up to 400 tape entries:

• c(400,4) — numeric: data length, start address, auto-start line, prog/vars length
• n$(400,13) — string: tape name/side label (user-supplied)
• t$(400,28) — string: header type (columns 1–17) and program name (columns 18–27)

The structured slicing of t$ is used consistently: t$(q,16 TO 27) gives the type+name region for brief listings, t$(q,18 TO ) gives the program name alone for searches. The type field is padded to 17 characters so that name data always starts at column 18.

Header Parsing

After the machine code call, BASIC reads header fields by sequential PEEK operations starting at address 64060. The variable a is used as a pointer, advancing through the header structure:

1. PEEK 64060 — header type byte (stored in s)
2. PEEK 64061 to PEEK 64070 — 10-character program name
3. Two-byte little-endian word: data length → c(n,1)
4. Two-byte little-endian word: start address (BYTES) or auto-start (PROGRAM) → c(n,2) / c(n,3)
5. Two-byte little-endian word: prog/vars length → c(n,4)

The little-endian decode idiom used throughout is PEEK a + 256 * PEEK (a+1), standard for this platform.

Key BASIC Idioms and Techniques

• Error handling: Line 5 uses ON ERR RESET (TS2068 extension) as a global guard. Line 55 resets it to ON ERR GO TO 5 so tape-read errors restart the menu rather than crashing.
• INKEY$ polling loop: Lines 85–98 loop without a PAUSE, relying on the fast polling of INKEY$; this is a busy-wait menu, which means only one keypress is needed (no ENTER required).
• Dual PRINT/LPRINT: Nearly every display line has a paired LPRINT statement on the next line number, allowing simultaneous screen and printer output throughout all listing options.
• Subroutine reuse: The tape-name listing block at lines 500–540 doubles as a subroutine (called via GO SUB 500 from line 200) and a standalone option. The dir flag at line 535 controls whether it returns or falls through to STOP.
• Array persistence: Option 4 relies on the arrays remaining in memory after a tape load. The program instructs the user to CLEAR 63999 before loading, which sets RAMTOP just below the machine code area, preserving the arrays at higher addresses while allowing the program itself to reload.

Bugs and Anomalies

• Line 9974 uses uppercase N as the loop variable (FOR N=1 TO 400), but lines 9977, 9988, 9989, 9994 reference lowercase n. On this platform BASIC variable names are case-sensitive for numeric variables only in some implementations; this may function correctly if the interpreter treats them as the same variable, but it is inconsistent coding.
• The loop at line 9974 runs FOR N=1 TO 400, but there is no explicit n counter that advances beyond the NEXT n at line 9995. The NEXT n at line 9995 increments the loop variable and then jumps back to GO TO 9975, bypassing the FOR statement — this effectively makes the loop counter increment on each pass but the GO TO re-enters the loop body directly, which may cause unexpected behavior if the loop counter ever reaches 400.
• Lines 300–340 (raw full header dump) are defined but not reachable from the menu; no menu option dispatches to line 300.
• The t$ array is dimensioned with 28 columns, but the type strings “NUMERIC ARRAY” (13 chars) and “CHARACTER ARRAY” (15 chars) padded to column 17 plus the 10-character name fit within 27 characters, leaving the 28th column unused.