This appears to be brand new and unused, but it might just have been looked after. The ribbon cable shown appears to be unconnected and still wrapped in its original tape (it’s been kept clean in a polythene bag for many years). I’ve no software or manual (yet…).

Originally the GM860 was supplied with a lead terminating in a Centronics printer plug. This allowed it to be connected directly to the printer port of a Gemini Galaxy or similar computer. Note that it isn’t compatible with a standard Centronics printer socket as all the PIO lines are directly connected so they are bi-directional. A diagram was given in the manual to show how it could be connected to a 26-way Nascom or Gemini PIO port without a Centronics connector.


Apart from the power switch there are no controls – it was software driven from the computer. It was capable of burning all Intel-compatible EPROMs from 2kBx8 (2716) up to 32kB x 8 (27256) in both 24-pin and 28-pin sizes. Address line A15 appears to be latched in IC10, but it isn’t connected so 64kB addressing isn’t implemented.


The EPROM supply voltage could be raised to 6V in order to use the “intelligent programming algorithm” for the larger EPROMs. This gives much higher programming speeds.

Software was provided on a disk in Gemini QDSS format, which could also be read by QDDS drives:

  • PROG.COM  The actual programming software
  • CPROG.COM  A configuration program for PROG.COM. This let you change the base address of the PIO and the default EPROM type at start-up.
  • PROGINIT.MAC  The low level assembly language drivers used in PROG.COM

There was an eight-page manual provided. This covered installation and how to use PROG.COM, but apart from that there was little information. No details were given on how to use the programmer with other software and there were no details of what was in the programmer.

PROG.COM displayed a comprehensive menu when run:

0 – Return to CP/M
1 – Change EPROM type
2 – Read EPROM into buffer
3 – Read a disk file into buffer
4 – Edit buffer contents
5 – Display buffer contents
6 – Write buffer to disk file
7 – Write buffer to EPROM
8 – Verify that EPROM is erased
9 – Verify EPROM against buffer contents

The heading displayed:
i) whether the buffer contained any data
ii) the EPROM type currently selected
iii) the name of the last file read/written to/from the buffer

And for the circuit diagram:  (Cheers Danny! 🙂 )