8721 PLA pinout

DIP-48. C128 address decode: ROM/RAM banks, chip selects, VIC and color RAM

The C128 address-decode PLA, not the C64 82S100. Makes /ROM1-/ROM4, /ROML, /ROMH, /CHAROM, /COLRAM, /VIC, /IOCS and the DRAM strobes from the address bus and the bank inputs LORAM, HIRAM, CHAREN and the cartridge lines. Runs in every mode, so a bad one looks like a dead machine or wrong banking. Pinout from the companion sheet, which flags this chip as reconstructed: verify before use.

Open the interactive PLA pinout

Pins

Pin	Name	Type	Signal
1	A15	addr	CPU address bit 15.
2	A14	addr	CPU address bit 14.
3	A13	addr	CPU address bit 13.
4	A12	addr	CPU address bit 12.
5	A11	addr	CPU address bit 11.
6	A10	addr	CPU address bit 10.
7	VICFIX	ctrl	Input that modifies CASENB latching for VIC timing.
8	DMAACK	ctrl	DMA acknowledge (sheet name).
9	AEC	ctrl	Address Enable Control from the VIC-IIe.
10	R/W	ctrl	Read/write from the CPU.
11	GAME	ctrl	Cartridge GAME line.
12	EXROM	ctrl	Cartridge EXROM line.
13	Z80 EN	ctrl	Labeled Z80 EN on the PLA, but it receives the Z80 BUSACK: HIGH/LOW says whether the Z80 has given up the bus. The real Z80 enable is MMU pin 43.
14	Z80 I/O	ctrl	Z80 input requesting I/O.
15	64/128	ctrl	Mode sense: 64 or 128.
16	I/O SE	ctrl	I/O select input from the MMU.
17	ROMBNKHI	ctrl	ROM bank select, high bit (sheet name).
18	ROMBNKLO	ctrl	ROM bank select, low bit (sheet name).
19	VMA4	ctrl	VIC memory address line 4 (sheet name).
20	VMA5	ctrl	VIC memory address line 5 (sheet name).
21	BA	ctrl	Bus Available from the VIC.
22	LORAM	ctrl	Processor port bit: LORAM (BASIC ROM select).
23	HIRAM	ctrl	Processor port bit: HIRAM (KERNAL ROM select).
24	VSS	ground	0 V.
25	CHAREN	ctrl	Processor port bit: CHAREN (character ROM or I/O select).
26	VA14	addr	VIC address 14 input from the 6526; selects the video bank in C64 mode.
27	128/256	ctrl	Mode sense: 128K or 256K.
28	N/C	nc	No connection.
29	/SDEN	ctrl	S-data buffer enable: turns on the buffer between the data bus and the S DATA bus.
30	/ROML	ctrl	Low ROM select.
31	/ROMH	ctrl	High ROM select.
32	CLRBNK	ctrl	Color RAM bank select output (C128 Service Manual p. 29).
33	/FROM	ctrl	Function ROM select.
34	/ROM4	ctrl	ROM 4 select.
35	/ROM3	ctrl	ROM 3 select.
36	/ROM2	ctrl	ROM 2 select.
37	/ROM1	ctrl	ROM 1 select.
38	/IOCS	ctrl	Enables the external I/O decoder for CIA1, CIA2, I/O1, I/O2, SID and the 8563 VDC. The VIC has its own select (pin 42).
39	DIR	ctrl	Data direction for the buffers.
40	DWE	ctrl	DRAM write enable.
41	CASENB	ctrl	Column address strobe enable.
42	/VIC	ctrl	VIC chip select.
43	/IOACC	ctrl	I/O access strobe.
44	/GWE	ctrl	Write enable for the color RAM, active LOW. DRAM writes use DWE (pin 40).
45	/COLRAM	ctrl	Color RAM chip select.
46	/CHAROM	ctrl	Character ROM select.
47	CLK	clock	Clock input.
48	VCC	power	+5 V supply.

Fitted in

Commodore 128 U11

Sources

C128 Service Manual, 8721 PLA pinout and pin description, p. 29