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Can you read a 82s100 PLA chip?

P

Pet Rescue

Experienced Member
Joined
Dec 15, 2010
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484
Location
Staffordshire, England
Hi All

Is there a way to read a 82s100 PLA chip that is in the C64 and 8296 Pet's with a willem programmer?

I have a dead 8296D and would like to verify the PLA chips before blowing a their replacements.
 
You're welcome! Yeah, I've used an EPROM as a PLA in C64's before with good success. Note that the adapter described there (for reading a PLA) will most likely *not* work if you actually are trying to program a real, blank, 82s100 chip. For that, I think you'll need a programmer that supports them. Of course, if you had a programmer that supported the chip, you wouldn't need an adapter to read it...

-Ian
 
Cheers RetroHacker!!

I've just used my last PLA to resurrect my newly aquired SX-64, it had a bit of a mental with flashing colours and mad sounds!!
It looks like I need a new source so my 27512's look a good option then. I now need to read the two PLA's in my 8296D to see if that is the problem on why it won't power up. Your info is very informative with both read and write adapters, looks like a busy night ahead!

Thanks again!!
 
I've had really really bad luck with the eprom replacement pla, unless you use a ST M27C512-90B6. I've used about 10 of these for repairs and had no issues, (Every c64 I've fixed I use a easyflash to test and the selftest for the easyflash passes just fine.) If I've tried using the TMS27512-150s I have or some other standard eproms some machines will boot, others will not. None have run correctly for any amount of time.

The ST M27C512-90B6 is still available at mouser but is now EOL also.


Later,
dabone
 
I don't remember specifically what parts I've used in the past, but I've had good luck. Any EPROM I have used would have been a re-used pull from something else. I don't believe I've ever actually *bought* new EPROMs, execpt in the rare case of 16 bit 27c160's or 322's. In the case that I had a part that didn't work as a PLA, I just tried another one.

-Ian
 
PLA vs EPROM

PLA vs EPROM

Replacing a PLA with an EPROM is a tricky business. By its nature an EPROM is a 'glitchy' device: The outputs are full of spikes as the address lines settle. This is not a problem in memory applications where the designers wait for the device to settle (access time) before reading the data lines. But when used as a combinational logic device in replacing a PLA, the glitches can reek havoc by looking like extra clock pulses, etc. This will happen when two or more inputs switch at close to the same time. I would think it would be somewhat hit and miss to get one to work. Possibly it would work at some room temperatures, voltage levels, etc and not at others.
 
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Pet Rescue said:
Thanks dave m and dabone for the replies I will let you know how they perform.

What is the equivalent to a PLA today apart from eproms?
Click to expand...

I'm not sure. A 22V10 PAL springs to mind, but it is in a 24 'skinny dip' package which is only 0.3" wide. It would make for a funny looking adapter. They come in re-programmable versions with UV windows and are readily available. It can handle the 8 outputs with enough pins left over for 14 inputs while the 82S100 has 16 input capability so the schematic would have to be checked to see if all 16 are used. If any of the outputs are fed back to the input array then the PAL can do that without use of extra pins.

A small problem is that the C64/PET logic equations for the 82S100 would have to be known or reversed engineered from the schematic or EPROM data. Basically the EPROM data is a capture of all combinations of inputs (addresses) even though most are not used. From the data responses, a truth table and therefore the equations can be worked out.

It sounds like a fun project and I would be happy to supply a programmed 22V10 if a solution can be found.
-Dave
 
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Thanks all for the help and thanks dave for the offer on the 22V10.

On my 8296 as I took out the PLA chips I noticed that UE6 and UE5 were the wrong way round. Anyway after building the read adapters I read both of the chips and they verified ok so I put them back in the right way around and partial success the 8296 chirped the chirp, but sadly no screen display.

I took off the back of the monitor and power is to it as the electron gun is glowing.

As an experiment on my 8296 I decided to blow an eprom to the contents of UE5 and made an adapter to use in the pet and when fitted hey Presto! it chirped!! So it looks like a good replacement!

On the display front could the 6454 be at fault for the non display or am I barking up the wrong tree?
 
Check all the resistors esp the wire wound low ohm one(s) to make sure they didn't open, I have had the glow still with one open replacing it restored video.
 
Pet Rescue said:
On the display front could the 6454 be at fault for the non display or am I barking up the wrong tree?
Click to expand...

It is possible the the 6545 is bad, but there are other reasons. If you have a voltmeter, check for pulse activity (greater than 0.6V and less than 4.0V) on H Drive, V Drive, and Video on the mainboard. This will do a lot to clear the 6545 of suspicion.
 
Pet Rescue said:
As an experiment on my 8296 I decided to blow an eprom to the contents of UE5 and made an adapter to use in the pet and when fitted hey Presto! it chirped!! So it looks like a good replacement!
Click to expand...

That is great. But if you ever want to buy the PLA, instead of the Signetics part number (82S100), try to find them under the Philips part number: PLS100 and you should have better luck. But hey, if the EPROM works, that solves the problem.
 
Success!!!

Well eventually, I checked the voltages in relation to the 6545 and they were around 4v on the horizontal and vertical drives and video on the mainboard.

But still no screen, then I noticed a one pin wasn't in the socket on the 6545 and thought yes that's the fault!!

Out of the socket it comes and a bit of a straighten and reseat the chip into place and arghh! still no picture!!

Then a quick turn on the brightness control (I thought I'd set it in the middle) and yes commodore basic 4.0 and ready prompt!!

Now on to my other 8296 to fix and after swapping a few chips in and out, the 6545 has gone and both PLA's read and were faulty. After the eprom experiment worked those aren't a problem but does anyone know a source for the 6545 crtc? but at least with those replaced it's a working Pet!!

Two pets in one day back running!! (well one but the other will be with a few parts!!)
 
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