Commodore 64 PLA Replacement PLA20V8

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SKU: PLA20V8 Category: Tags: , , , ,

The PLA chip in the Commodore 64 is a common failing point today. The PLA or Programmable Logic Array is a computer chip that handles the memory map and the bank switching of the Commodore 64.

Along comes Daniël Mantione who designed this handy device to replace the original PLA chip compatible in most Commodore 64 computers.

Some frequently asked questions1,

Does Epyx Fastload work?
Yes, it works fine. The Epyx Fastload cartridge is a rather questionable design that performs analog tricks on digital lines. In order for the Epyx Fastload to work, a PLA needs to have similar analog properties and be stable at the border voltage between 0 and 1. This is the case for the GAL20V8B.

Does it work in all C64 mainboards?
Yes, except for the shortboard assy 250469 of course, because it uses a completely different type of chip. Assy 326298, 250407, 250425, 250466, 251103 (SX64), and C64 Reloaded MK1 have been tested. Assy 250441 and KU-14194HB have not been tested yet, but from what I know about these boards, I am confident about compatibility. Both PAL and NTSC tests have been done.

Can I use an alternate KERNAL?
Yes! An alternate KERNAL cartridge is a real PLA torture because a KERNAL cartridge changes the C64 mode two times within a half cycle and thus likes a responsive PLA. This has been tested both with the 1541 Ultimate II and with the Easyflash 3 and works perfectly.

Does Super-Zaxxon work?
Yes, it does work perfectly! Super-Zaxxon switches banks by means of accesses to the address lines of the C64 and as such, noise on the C64 address lines can cause undesired bank switches. This is a particular concern for EPROMs, which are known to cause switching noises on address changes. The way the GAL20V8 works, with an AND array and an OR array just like the original PLA, this kind of noise is not expected and indeed, the cartridge works perfectly.

More information about the PLA20V8 can be found here.
More information about the PLA can be found here.

1 - copied from Daniël Mantione's website.

Additional information

Weight 2 oz

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  1. One person found this helpful

    Question

    trebonse

    A couple of questions, is this the same soldering kit that is available on Daniël Mantione’s website? Also, are the two gal chips pre-programmed? I’m looking to replace a bad PLA but I do not have the tools to program the chips myself.

    (1) (0)

    Something wrong with this post? Thanks for letting us know. If you can point us in the right direction...

    • Admin 8-Bit Classics

      It is the same kit but it comes fully assembled and GAL chips come fully programmed.

      (0) (0)

      Something wrong with this post? Thanks for letting us know. If you can point us in the right direction...

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