VIC-20 Technical Section

VIC-20 Board Information

Schematics, Component layouts and port/connector pin-outs

Title Description Date
Ports and Pinouts A complete description of all the VIC-20's ports and their pinouts -
6502 Data Sheet The original data sheet for the CPU in the VIC-20, by Rockwell -
Internal 32K Memory Expansion How to expand the VIC's memory to 32K inside the case -
VIC-20 3/8/16/24K Memory Expansion A circuit diagram for an external switchable memory expansion with two ICs: a 74LS11 triple 3-input AND, and a 62256 SRAM. Designed by William Levak ( -
1541 Troubleshooting and Repair Some excellent tips on identifying the root cause of 1541 drive issues -
List of Commodore Hardware Not directly VIC-20-related, but a great list all the same ;-) By Jim Brain and Bo Zimmerman 23rd October 2007
VIC Technical Information A ZIP file containing some techie info on the VIC-20 -
Diagnostic cartridge Information about diagnostic carts available for Commodore computers.  
VIC-20 Troubleshooting Information from Ray Carlsen, of Carlsen Electronics on how to diagnose problems with your VIC-20  
VIC Chip Information on the VIC chip found in the VIC-20 2012


VIC-20 Firmware

Disassembly of ROM code and other firmware-related articles.

Title Description Date
NTSC-B and PAL firmware ROM differences A 'diff' between the ROMs in hex, along with some info -
1541C to 1541-II firmware differences A 'diff' between the ROMs in hex, along with some info, by Wolfgang Moser 1st March 2003
SpeedDOS Firmware Instructions for adapting the SpeedDOS firmware for the 1541-II  
VIC-20 Memory Map with corrections The memory maps used by the VIC-20 operating system, by Sam Laur 2nd March 1994
Raw VIC-20 Memory Map Original dumped memory map from the VIC-20 ROM 1st September 1994


Original documents written by third-party manufacturers of Commodore peripherals.

Title Description Date