Next step is to check they work exactly as the originals.

I wired my device programmer to a plugblock, to rearrange the signals as a 16 kbyte EPROM (27C128). 

The single-core wires are a bit stiff, the trick is to put them into the ZIF socket first then get the socket to grab them. Then you can bend them into the plug-board holes. A bit Tricky swapping chips under the wires though. I'll have to make something more robust.

I then read the original and recreated logic outputs. Alas, they did not match! Not a disaster, just need to figure it out.

2025-11-02

I put the fuse maps into a spreadsheet for comparison. I was pleased to see the main logic fuses match, so there is no error in the equations. The GAL chip has extra fuses for configuration, and the PAL does not, so they have nothing to compare with. 

The configuration bits seemed plausible. So I made a better test adaptor using a USB-to-I2C device and a I2C-to-digital-IO chip. It looks like this:

Top right, a USB-to-I2C module. Top centre, in I2C to 16-bit I/O module. Top left, an LED bar for monitoring the logic chip outputs. Bottom, an ATF16V8 being read to confirm that its outputs match the PAL14L4 which was read earlier. Sorry about the camera trying to focus more on the ribbon cable than the active components.

2025-11-13

I read the outputs of the PAL and the GAL chips. I found that for both type of chips, pins 16 and 17 behaved identically. Pins 14 and 15 of the GAL chips were low all the time, exactly as expected from the JEDEC files read from the PAL chips.

However, pins 14 and 15 of the PAL chips were not low all the time! It is rather suspicious that the same two pis on two different chips just happen to be unused. I suspect my device programmer is not reading out the fuses for the PAL14L4. Damn! I hope this is just a bug in the software and not hardware fault in my programmer.

On the plus side, I have now read out the actual behaviour of the PAL pins and therefore I should be able to reverse-engineer the logic equations from that. This will take time, but the Memotech version might provide a few hints.

2025-11-15

After a lot of manual work, I now have the GAL chips behaving exactly like the PAL chips. Success!