Spark Logic

Commodore 64 user port connection guide

Commodore 64 user port 24-contact user port wiring guide with power, signal assignments, and bench checks.

24-contact user port

24 contacts Current package

Commodore · 12 positions × 2 sides · keyed PCB edge

Identify the edge connector and ground

Required

Turn the computer off and identify the numbered and lettered faces from the rear view in the manual. Use an insulated keyed breakout and locate a digital ground contact.

  • Digital ground

Bench checks

  • Confirm the breakout maps to the correct side and key position.
  • Use the computer’s normal power source. Leave the breakout supply contacts disconnected.

Commodore 64 Programmer’s Reference Guide, Appendix I, User Port

Connection scenarios

Observe one parallel output

Connect a high-impedance scope probe to contact C and its return to A. Use the 6526 CIA 2 data direction and output registers to toggle bit 0 while preserving the other bits.

Bench checks

  • Use $DD03 for the port B direction register and $DD01 for port B data.
  • Check that the voltage changes when the selected bit toggles. Restore the original register values when finished.

Commodore 64 Programmer’s Reference Guide, Appendix I, User Port

24-contact user port wiring map

Highlighted contacts are used in the required step or selected circuit. Select a contact to inspect it.

Diagram rotated to show both contact rows. Numbers are the upper side. Letters are the lower side. Match the keyed connector to the rear view in the manual.
Selected pin details

D · PB1

Programmable I/O · Bidirectional

6526 CIA 2 parallel data bit. Select its direction in the data direction register.

Commodore 64 Programmer’s Reference Guide, Appendix I, User Port

Electrical limits · Pin in the reference

Models and documents

The map covers the external 24-contact user port. The signal roles and supply contacts are specific to the C64 shown in the manufacturer guide.

Commodore 64
User-port connector in the cited manufacturer documentation.