The VIC-20 memory expansion port is a 44-pin (22 per side) edge connector located on the left side of the computer, introduced with the VIC-20 in 1980 and documented in the VIC-20 Programmer’s Reference Guide (Commodore Business Machines and Howard W. Sams, 1983). It exposes a 14-bit address bus (CA0–CA13), an 8-bit data bus (CD0–CD7), and block-select lines (BLK1, BLK2, BLK3, BLK5) that map RAM cartridges into the 6502 address space, alongside separate read/write signals for the VIC video chip (VR/W) and the CPU (CR/W). Although the connector is physically the same 44-pin form factor used by the Commodore 64 expansion port, the signal set is entirely different and the two systems’ cartridges are electrically incompatible.
44 pin Connector at the Computer.
| Pin | Name | Description |
|---|---|---|
| A | GND | Ground |
| B | CA0 | Address 0 |
| C | CA1 | Address 1 |
| D | CA2 | Address 2 |
| E | CA3 | Address 3 |
| F | CA4 | Address 4 |
| H | CA5 | Address 5 |
| J | CA6 | Address 6 |
| K | CA7 | Address 7 |
| L | CA8 | Address 8 |
| M | CA9 | Address 9 |
| N | CA10 | Address 10 |
| P | CA11 | Address 11 |
| R | CA12 | Address 12 |
| S | CA13 | Address 13 |
| T | I/O 2 | Decoded I/O block 2, starting at $9130 |
| U | I/O 3 | Decoded I/O block 3, starting at $9140 |
| V | S02 | Phase 2 System Clock |
| W | /NMI | Non maskable Interrupt |
| X | /RESET | 6502 Reset |
| Y | n/c | Not connected |
| Z | GND | Ground |
| 1 | GND | Ground |
| 2 | CD0 | Data 0 |
| 3 | CD1 | Data 1 |
| 4 | CD2 | Data 2 |
| 5 | CD3 | Data 3 |
| 6 | CD4 | Data 4 |
| 7 | CD5 | Data 5 |
| 8 | CD6 | Data 6 |
| 9 | CD7 | Data 7 |
| 10 | /BLK 1 | BLK 1 (Memory location $2000 - $3fff) |
| 11 | /BLK 2 | BLK 2 (Memory location $4000 - $5fff) |
| 12 | /BLK 3 | BLK 3 (Memory location $6000 - $7fff) |
| 13 | /BLK 5 | BLK 5 (Memory location $a000 - $bfff) |
| 14 | RAM 1 | RAM 1 (Memory location $0400 - $07ff) |
| 15 | RAM 2 | RAM 2 (Memory location $0800 - $0bff) |
| 16 | RAM 3 | RAM 3 (Memory location $0c00 - $0fff) |
| 17 | V R/W | Read/Write from Vic chip (1=R, 0=W) |
| 18 | C R/W | Read/Write from CPU (1=R, 0=W) |
| 19 | /IRQ | 6502 Interrupt Request |
| 20 | n/c | Not connected |
| 21 | +5V | +5 VDC |
| 22 | GND | Ground |