Author Topic: Help with converting old PALs to GAL  (Read 701 times)

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Offline Emulator III

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Help with converting old PALs to GAL
« on: July 30, 2022, 12:31:33 am »
Hi there,

I am trying to restore an old piece of audio hardware, which incidentally is the same model as my user name. It is a digital sampling keyboard which was made in the late 1980's

The trouble which I (and others) are having is that the unit is full of old custom PALs right through the logic and computer circuits. Some of these are failing.

I have been working with another user trying to read and write some of the PALs. We think we've been successful in reading some so far and have some JED files generated from them.

However I've been struggling with the next step, which is trying to write them back into newer GAL chips. I have the trusty TL866 II programmer which does seem to write the chips OK. I can read back the data and verify after writing. But I still can't get them to actually function in the host machine.

I was wondering if anyone could assist who has had some experience dealing with this sort of problem? Anyone here successfully ported old PAL22V10 over to GAL22V10? I can provide the JED files we have so far if anyone would be so kind to take a look at them?

Thanks for your time
Regards
Luke (EIII)
 

Offline up8051

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Re: Help with converting old PALs to GAL
« Reply #1 on: July 30, 2022, 02:08:00 pm »
PAL22V10 and GAL22V10 should have the same Fuse Map, so the JED file matches both types.
However, first check that the chips are not read-protected. Then you will read JED but there will be no data in it.
 

Offline Emulator III

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Re: Help with converting old PALs to GAL
« Reply #2 on: August 02, 2022, 12:00:50 pm »
Hi up8051,

Great name by the way! Have had many years repairing circuits with the 8051 at the core!

Interesting as I thought there would have to be some process to port the JED over, such as the PALtoGAL.

Anyway it's looking like the JED files are no good, or the chips are protected. It's not reading only 1's but it looks pretty rubbish.

Can anyone advise on any other current methods to to read a PAL22V10?

Thank you for your input
Cheers
Luke
 

Offline up8051

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Re: Help with converting old PALs to GAL
« Reply #3 on: August 02, 2022, 12:24:30 pm »
Show the readout JED file.

Converting from PAL (for example PAL16L8  to GAL16V8)  do GAL path is:

1 Read JED file
2 Convert JED to equations (JED2EQN tools)
3. Recompile to GAL target

If PAL is protected that only path is reverse engineering.
Service manual for Emulator III is available so there may be a lot of useful information.
 

Offline Emulator III

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Re: Help with converting old PALs to GAL
« Reply #4 on: August 02, 2022, 12:41:55 pm »
Hi up8051,

Thanks for the prompt reply.

I see, so you do have to reverse to equation and then re-compile? I was trying to use PAL to GAL but no idea if I was using it correctly... I am completely new to this world but trying to learn to save our EMU's!

Please see the JED attached. Let me know if you need anything further.

Cheers
Luke
 

Offline Andy Watson

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Re: Help with converting old PALs to GAL
« Reply #5 on: August 02, 2022, 12:53:55 pm »
Anyway it's looking like the JED files are no good, or the chips are protected. It's not reading only 1's but it looks pretty rubbish.

From AMD's datasheet:
Quote
When the security fuse is programmed, the array will read as if every fuse is programmed ...
Looks as if the devices have been secured.
 

Offline Emulator III

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Re: Help with converting old PALs to GAL
« Reply #6 on: August 02, 2022, 01:08:08 pm »
Hi Andy,

Thanks for your input. Did you have a look at the file? Does that indicate to you that every fuse is programmed, and hence, it is secured?

As I said, very new to the world of PAL but I'm learning! I actually just reversed this one into the equations using jedutil! Which I thought was quite an achievement... hah

Cheers
Luke
[attachimg=1]
 

Offline Andy Watson

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Re: Help with converting old PALs to GAL
« Reply #7 on: August 02, 2022, 02:40:46 pm »
There are ones and zeros in the fuse map - so it's probably not due to the security fuse. However, the map does not make sense. I would expect to see mostly zeros with the odd one here and there. In particular, there are whole rows set to one - this would imply that some of logic AND gates are connected to every possible input. Since both true and ccomplement inputs are present - it doesn't make sense.  I would say it's gibberish. Are you sure you have the right algorythm for reading the device?

 

Offline up8051

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Re: Help with converting old PALs to GAL
« Reply #8 on: August 02, 2022, 06:17:38 pm »
There are many PALs

IC10 PAL16L8
IC27 PAL16L8

IC11 PAL16R4
IC32 PAL16R4
IC4 PAL16R8
IC5 PAL16R8
IC6 PAL16R8
IC7 PAL16R8
IC33 PAL22V10
IC50 PAL20R8
IC47 PAL16R4

Only first two are combinational logic (easy to reverse), the rest are registered (more difficult to reverse)
 


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