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.
1 – copied from Daniël Mantione’s website.
Specification: Commodore 64 PLA Replacement PLA20V8