PLA (C64 chip)

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Disambiguation The title of this article is ambiguous. 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, neatPLA, PLA20V8 (aka "GAL-PLA") and also PLAs based on eproms as a replacement part.

Pinout[edit | edit source]

Pinout of the PLA
Pin Name Remarks
1 FE/NC Used for programming field-programmable parts and not connected internally for mask programmable parts.[1]
2 I7 Connected to A13 of the address bus
3 I6 Connected to A14 of the address bus
4 I5 Connected to A15 of the address bus
5 I4 Connected to #VA14 on VIC-II
6 I3 Connected to #CHAREN on I/O port of the 6510 CPU
7 I2 Connected to #HIRAM on I/O port of the 6510 CPU
8 I1 Connected to #LORAM on I/O port of the 6510 CPU
9 I0 Connected to #CAS on the VIC-II
10 F7 #ROMH
11 F6 #ROML
12 F5 #I/O
13 F4 GR/#W, connected to #WE on the color RAM
15 F3 Connected to #CS1 on the #CHAROM
16 F2 Connected to #CS on the #KERNAL ROM
17 F1 Connected to #CS on the #BASIC ROM
18 F0 #CASRAM, connected to the #CAS pin on the DRAM
19 #CE Chip Enable
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 Connected to R/#W of the bus
25 I10 #AEC, connected to inverted version of AEC on the VIC-II
26 I9 Connected to BA on the VIC-II
27 I8 Connected to A12 of the address bus
28 VCC +5V

Links[edit | edit source]

References[edit | edit source]

  1. Thomas ’skoe’ Giesel, The C64 PLA Dissected, PDF, section 3.2