ROM-81

An EPROM found in a Cambridge Microelectronics ROM-81 unit, with “1678” written on its label. It is a 2K (2716-type) EPROM that sat in socket B and decodes to address 14336 (3800h) on the ZX81/TS1000. It holds a tape filing utility: RAND USR 14336 asks “INPUT FILE NAME”, then “INPUT COMMAND”. Its other messages are INPUT ADDRESS, INPUT LENGTH, START TAPE, STOP TAPE, ERROR, INPUT DIM VARIABLE and a directory heading “FILE NAME TYPE LENGTH START”, which suggests it saves and loads named blocks of memory and arrays.

What’s in the download

• Camel.BIN: the 2,048-byte EPROM image.
• Camel_ROM-81.txt: notes on the board, socket, address and prompts.
• Camel.txt: a z80dasm disassembly of the image.
• Camel_F.jpg and Camel_R.jpg: photos of the board.

Program Analysis

The same routine, with the same messages at the same offsets, makes up the first 2K of EPROM #1 of the Hot Z-II 48-64K set (#56068). The two differ in about 320 bytes: mostly address high bytes (38h here, C0h–C7h there), plus calls to the ROM’s FAST and SLOW routines that are present here and replaced by NOPs in the Hot Z-II copy. This copy appears to be the same tape filing utility assembled to run at 3800h. Who wrote it is not shown in the image.

Potential Issues

• Camel.txt was disassembled with origin 2000h, but the code runs at 3800h (its first instruction is JP 3872h), so the addresses in that listing are 6K too low.

Related Products

ROM-81

Store useful routines and commonly used information in EPROM. Accepts either 2716 or 2732 EPROMs to allow up to 8K of memory in 2K byte increments.

Image Gallery

Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.