November 25, 2022

Programmable devices: Jedec files

If you are working with PAL or GAL devices, you will end up dealing with a "jedec file". This is an ascii file (sort of, almost) that device programmers yield when reading out a device, or accept in order to program one.

My current interest is in a jedec file that was sent me for the SAC-201 ISA bus board. This board was used in an old ISA bus computer to talk to the 25 pin cable that connected to a MOD-EMUP programmer.

Up to now, I have always just glanced at these files as they come and go from my device programmer. In days gone by I have read out PAL/GAL devices, then used PALASM to disassemble them into logic equations. Jedec files are just a lot of zeros and ones, and are by no means intended for human consumpion. The logic equations tell the story of what the device does.

I used to use PALASM on a machine running DOS to do the disassembly and this worked just fine. Right now though, that machine is in the back of a shed somewhere and I would much prefer to use my linux machine to do the translation. If nothing else, getting files into and out of my DOS machine (running FreeDOS) was never an easy business. I tried using Dosemu on my linux machine and spent some time setting it up and installing PALASM-4 on it, but it always rejects my Jedec files with some complaint about the files being invalid. My actual DOS machine runs an older "Beta" version of PALASM and seems to accept any Jedec file I throw at it.

Jedec file format

This seems to be well documented. The file has two unprintable characters in it, namely 0x02 and 0x03 (STX and ETX). These more or less indicate the beginning and end of the file. They also play hob with tools like unix2dos.

Have any comments? Questions? Drop me a line!

Programmable devices /