PLA (C64 chip)
The Programmable Logic Array (PLA) is a hardware programmable chip in the C64 which only contains combinatorial logic.
Designed by Dave DiOrio, the PLA is used to create chip select signals received from various other signals. These signals control which chip is to be connected to the data bus. Therefore the PLA is responsible for dictating the memory map of the C64 and enables the implementation of bank switching. Commodore engineer James Redfield said it was the "glue logic to tie everything together". The final version of the PLA logic was REV3.
This chip is failure prone, especially the earliest models. Eventually, the third party PLAs were created, such as the SuperPLA, realPLA, U17 PLAnkton, PLAtinum and also PLAs based on eproms as a replacement part.
|5||I4||Connected to #VA14 on VIC-II|
|6||I3||Connected to #CHAREN on I/O port of 6510|
|7||I2||Connected to #HIRAM on I/O port of 6510|
|8||I1||Connected to #LORAM on I/O port of 6510|
|9||I0||Connected to #CAS on VIC-II|
|20||I15||Connected to VA12 on VIC-II|
|21||I14||Connected to VA13 on VIC-II|
|22||I13||Connected to #GAME on pin 8 of cartridge port|
|23||I12||Connected #EXROM on pin 9 of cartridge port|