GND	1  •	40	CA1
PA0	2	39	CA2
PA1	3	38	IRQA
PA2	4	37	IRQB
PA3	5	36	RS0
PA4	6	35	RS1
PA5	7	34	RESET
PA6	8	33	D0
PA7	9	32	D1
PB0	10	31	D2
PB1	11	30	D3
PB2	12	29	D4
PB3	13	28	D5
PB4	14	27	D6
PB5	15	26	D7
PB6	16	25	E
PB7	17	24	CS1
CB1	18	23	CS2
CB2	19	22	CS0
Vcc	20	21	R/W

Pin	Symbol	Description
1	GND	ground
2	PA0	port A
3	PA1	port A
4	PA2	port A
5	PA3	port A
6	PA4	port A
7	PA5	port A
8	PA6	port A
9	PA7	port A
10	PB0	port B
11	PB1	port B
12	PB2	port B
13	PB3	port B
14	PB4	port B
15	PB5	port B
16	PB6	port B
17	PB7	port B
18	CB1	peripheral control (port B)
19	CB2	peripheral control (port B)
20	Vcc	supply voltage
21	R/W	read/write
22	CS0	chip select (active high)
23	CS2	chip select (active low)
24	CS1	chip select (active high)
25	E	clock
26	D7	data bus
27	D6	data bus
28	D5	data bus
29	D4	data bus
30	D3	data bus
31	D2	data bus
32	D1	data bus
33	D0	data bus
34	RESET	master reset (active low)
35	RS1	register select (address bus)
36	RS0	register select (address bus)
37	IRQB	interrupt output (active low)
38	IRQA	interrupt output (active low)
39	CA2	peripheral control (port A)
40	CA1	peripheral control (port A)

Specifications
(typical values under recommended operating conditions, unless specified)

Parameter	Value	Unit
Max. clock frequency	1 (6821) 1.5 (68A21) 2 (68B21)	MHz
Pulse width, E low	430 (6821) 280 (68A21) 210 (68B21)	ns
Pulse width, E high	450 (6821) 280 (68A21) 220 (68B21)	ns
Min. RESET pulse length	1	µs