PLA (C64 chip)

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Disambiguation The title of this article is plurivalent. May also refer to (PulL Accumulator from stack).
PLA Chip 1988, Commodore No. 906114-01

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.


Pinout of the PLA
Pin Name Remarks
2 I7
3 I6
4 I5
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
10 F7
11 F6
12 F5
13 F4
14 VSS
17 F1 #BASIC
19 #CE
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
24 I11
25 I10
26 I9
27 I8
28 VCC