Commodore 64 (C64) forums

As some of you may have noticed, over the last 2 years, I have invested time and energy developing replacements for a few custom chips used in Commodore 8 bit computers.

These include:
- PLAnkton which replaces the C64/SX-64 programmable logic array 906114-01 or 251064-01
- TOLB which replaces the 7701/8701 clock generator used on later C64 boards, the C64c and the C128
- GandALF which replaces the 1541 custom controller and array 325572-01

I am presently considering the possibility of making PLA replacements for the C64c board 250469, specifically part no. 251715-01. Board 250469 can use 2 different types of PLA which incorporates most of the glue logic ICs used in the original C64 and they are part no. 251715-01 and 252535-01. Making PLA 252535-01 may prove too difficult because it incorporates the 512x4 bits color RAM and this type of chip is no longer in production.

So far, I did not make this substitute strictly because there doesn't seem to be much interest, not because there are any technical hurdles I can't overcome. This variant of the PLA is based on more modern technology than the one employed on 28 pin PLAs and it doesn't produce any discernable heat so it fails far less frequently.

I would like the people of Melon64 to indicate if there is, in fact, sufficient interest to make a substitute for PLA 251715-01 used on board 250469 and how much people would expect to pay for this replacement.

Thank you all for your feedback.

- Francois

Would it be available at the same price as the PLAnkton, would you have an EU distributor, and can we get to name it the PLAtypus?

If (at least) the first two are true, I'm in for two units.

Stealth wrote: ↑Tue Nov 28, 2017 6:03 pm Would it be available at the same price as the PLAnkton, would you have an EU distributor, and can we get to name it the PLAtypus?

If (at least) the first two are true, I'm in for two units.

It can't be offered at the same price as PLAnkton because there is a lot more technology involved. The PLA used in breadbin C64 is 28 pins and represents a single 24V10 logic array. The large PLA in the C64c is a 64 pins IC which carries all the logic of the original PLA as well as the functions of half a dozen 74 series logic ICs used for glue logic.

No, we can't name it PLAtypus because this name was associated with an EPROM based project.

Yes, there will be EU distributors. Poly Play presently distributes PLAnkton, TOLB and GandALF.

I would be interested in two units.

SteveO wrote: ↑Wed Nov 29, 2017 5:32 pm I would be interested in two units.

Looks like I will be doing this project after all.

Weren't there two versions of this later PLA? There seem to be several revisions of this motherboard.

From https://www.c64-wiki.com/wiki/C64C

"The PLA chip and some TTL chips have been integrated into a 64 pin chip (251715-01 or 252535-01). The "252535-01" contains the color RAM as well."

I can't really verify this information, I have a 64C with an earlier board with the 64Kx4 chips but the 28 pin PLA... Oh well.

I guess I don't have a horse in this race!

Gyro Gearloose wrote: ↑Thu Nov 30, 2017 1:57 am Weren't there two versions of this later PLA? There seem to be several revisions of this motherboard.

From https://www.c64-wiki.com/wiki/C64C

"The PLA chip and some TTL chips have been integrated into a 64 pin chip (251715-01 or 252535-01). The "252535-01" contains the color RAM as well."

I can't really verify this information, I have a 64C with an earlier board with the 64Kx4 chips but the 28 pin PLA... Oh well.

I guess I don't have a horse in this race!

Ha hum... from original post...

Board 250469 can use 2 different types of PLA which incorporates most of the glue logic ICs used in the original C64 and they are part no. 251715-01 and 252535-01. Making PLA 252535-01 may prove too difficult because it incorporates the 512x4 bits color RAM and this type of chip is no longer in production.

eslapion wrote: ↑Wed Nov 29, 2017 12:48 pm It can't be offered at the same price as PLAnkton because there is a lot more technology involved. The PLA used in breadbin C64 is 28 pins and represents a single 24V10 logic array. The large PLA in the C64c is a 64 pins IC which carries all the logic of the original PLA as well as the functions of half a dozen 74 series logic ICs used for glue logic.

Okay, that's reasonable enough.

eslapion wrote: ↑Wed Nov 29, 2017 12:48 pm No, we can't name it PLAtypus because this name was associated with an EPROM based project.

Back to the dictionary with me, then.

eslapion wrote: ↑Wed Nov 29, 2017 12:48 pm Yes, there will be EU distributors. Poly Play presently distributes PLAnkton, TOLB and GandALF.

Works for me. Sign me up for two, please.

Stealth wrote: ↑Thu Nov 30, 2017 9:04 am Back to the dictionary with me, then.

A name has already been chosen...

eslapion wrote: ↑Thu Nov 30, 2017 6:12 am
Ha hum... from original post...

Board 250469 can use 2 different types of PLA which incorporates most of the glue logic ICs used in the original C64 and they are part no. 251715-01 and 252535-01. Making PLA 252535-01 may prove too difficult because it incorporates the 512x4 bits color RAM and this type of chip is no longer in production.

LOL yes I see now. I was too busy digging in the closet for my 64C (next week on Hoarders!) and taking it apart to fully read your post...