The Commodore parallel cable

for Commodore 1541 drives

You should follow these instructions if you want to connect the cable directly onto the periphery chip in the drive.

Important notes

  • Because you will solder a cable onto some pins of the VIA#1 chip inside the drive, you will have to first make sure that these pins are not used for any other purpose. What you need to do depends on the version of the drive you have:
    • In original Commodore 1541 drives, nothing is defined to any of the bits of Port A. You can solder the cable without any problem.
    • In 1541C drives, bit 0 of Port A is used for the detection of the head being over track 1. After stripping this connection off of the chip, you will have to replace the DOS ROM with that of the 1541 or the 1541-II. Otherwise you'll get strange results when the drive is seeking: the DOS tries to rely on the detector line which doesn't exist anymore.
    • In 1541-II drives, bit 0 of Port A is grounded, strip this connection off of the chip.


You need the following parts to build this cable:

  • One solderable user port plug
  • A shielded or unshielded 10-wire cable of, preferably at most, 2 meters

Step 1. Solder one end of the cable right onto the VIA#1 periphery chip inside the drive.

Step 2. Solder the other end of the cable onto the user port plug. You should have the following connections:

VIA#1 User port plug
  2, PA0  C, PB0
  3, PA1  D, PB1
  4, PA2  E, PB2
  5, PA3  F, PB3
  6, PA4  H, PB4
  7, PA5  J, PB5
  8, PA6  K, PB6
  9, PA7  L, PB7
 18, CB1  8, PC2
 39, CA2  B, FLAG2
not connected  A, GND

Circuit diagram:

[Commodore parallel cable for 1541 drives]

You can find the description of all parts used on the diagrams at the legend page.

Source: The Joe Forster-STA homepage