6526 CIA pinout

DIP-40. Keyboard, joysticks, serial, user port

CIA1 at $DC00 (keyboard, joysticks, /IRQ). CIA2 at $DD00 (serial bus, user port, /NMI). Two of these on a C64. The timers and the TOD clock are on the same chip.

Open the interactive CIA pinout

Pins

Pin	Name	Type	Signal
1	Vss	ground	0 V.
2	PA0	io	Port A bit 0. C64 CIA1: keyboard column out and control port 2. CIA2: VIC bank select.
3	PA1	io	Port A bit 1. C64 CIA1: keyboard column out and control port 2. CIA2: VIC bank select.
4	PA2	io	Port A bit 2. C64 CIA1: keyboard column out and control port 2. CIA2: RS-232 data out (user port M).
5	PA3	io	Port A bit 3. C64 CIA1: keyboard column out and control port 2. CIA2: serial bus.
6	PA4	io	Port A bit 4. C64 CIA1: keyboard column out and control port 2. CIA2: serial bus.
7	PA5	io	Port A bit 5. C64 CIA1: keyboard column out. CIA2: serial bus.
8	PA6	io	Port A bit 6. C64 CIA1: keyboard column out. CIA2: serial bus.
9	PA7	io	Port A bit 7. C64 CIA1: keyboard column out. CIA2: serial bus.
10	PB0	io	Port B bit 0. C64 CIA1: keyboard row in and control port 1. CIA2: user port.
11	PB1	io	Port B bit 1. C64 CIA1: keyboard row in and control port 1. CIA2: user port.
12	PB2	io	Port B bit 2. C64 CIA1: keyboard row in and control port 1. CIA2: user port.
13	PB3	io	Port B bit 3. C64 CIA1: keyboard row in and control port 1. CIA2: user port.
14	PB4	io	Port B bit 4. C64 CIA1: keyboard row in and control port 1. CIA2: user port.
15	PB5	io	Port B bit 5. C64 CIA1: keyboard row in. CIA2: user port.
16	PB6	io	Port B bit 6. C64 CIA1: keyboard row in. CIA2: user port.
17	PB7	io	Port B bit 7. C64 CIA1: keyboard row in. CIA2: user port.
18	/PC	ctrl	Peripheral control strobe. Pulses when port B is written.
19	TOD	io	Time-of-day clock input (50/60 Hz tick).
20	Vcc	power	+5 V supply.
21	/IRQ	ctrl	Interrupt request. On the C64, CIA1 drives /IRQ and CIA2 /NMI.
22	R/W	ctrl	Read/write from the CPU.
23	/CS	ctrl	Chip select (address decoding). On the C64: CIA1 at $DC00, CIA2 at $DD00.
24	/FLAG	ctrl	Flag input. Edge-triggered interrupt input.
25	Φ2	clock	Phase 2 system clock input.
26	D7	data	Data bus bit 7.
27	D6	data	Data bus bit 6.
28	D5	data	Data bus bit 5.
29	D4	data	Data bus bit 4.
30	D3	data	Data bus bit 3.
31	D2	data	Data bus bit 2.
32	D1	data	Data bus bit 1.
33	D0	data	Data bus bit 0.
34	/RES	ctrl	Reset. LOW clears the CIA.
35	RS3	addr	Register select bit 3.
36	RS2	addr	Register select bit 2.
37	RS1	addr	Register select bit 1.
38	RS0	addr	Register select bit 0.
39	SP	io	Serial port shift register I/O.
40	CNT	io	Counter clock input/output for the timers.

Fitted in

Commodore 64 U1 (CIA1), U2 (CIA2)
Commodore 128 U1, U4
Commodore 1571 disk drive U20 (6526A or 8520; fast serial at $4000)

6526 CIA pinout

Pins

Fitted in

Sources