Commodore VIC-20 Programmer's Reference Manual page 258

This port is used for expansions of the VIC system which require
access to the address bus or the data bus of the computer. Caution
is necessary when using the expansion bus, as it is possible to
damage the VIC by malfunctioning user equipment,
The signals available on the connector are as follows:
NAME PIN # DESCRIPTION
GND
CDO
CD1
CD2
CD3
CD4
CDS
CD6
CD7
BLK1
BLK2
BLK3
BLK5
RAM1
RAM2
RAM3
VR/W
CRW
1
2
3
±
5
6
7
a
9
10
11
12
13
14
15
16
17
18
IRQ
(NC)
+ 5V
GND
GND
CAO
CA1
CA2
CA3
CA4
13
20
21
22
A
e
c
D
E
F
System ground
Data bus bit 0
Data bus bit 1
Data bus btt 2
Data bus bit 3
Data bus bit 4
Data bus Dit 5
Data bus bit 6
Data bus bit 7
SK decoded RAM/ROM block 1T @ S2000
(active low)
SK decoded RAM ROM block 2, @ S4000
(active low)
BK decoded RAM.'ROM block 3, (a S6000
(active low)
8K decoded ROM block 5. (a SAO0O
(aclive low)
1K decoded RAM block, (a S0400
(active low)
1K decoded RAM block @ S0800
(active low)
1K decoded RAM block (5 SQCOO
(active low)
Read Write line from VIC chip
(higrweadr low-write)
Read Write Eine from CPU
(high-read, low-write)
Interrupt Request line to 6502 [active low)
i
Address bus bit 0
Address bus bit 1
Address bus bit 2
Address bus bit 3
Address bus bit 4
I
I
I
i
I
I
i
242
I