The XMP1541 cable combo

Important notes

  • You definitely need 1N5819 or BAT85 for this cable, other Schottky-diodes or the usual 1N4148 diodes don't work with many motherboards.
  • 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. This 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.

Construction

First, create the parallel port for 1541 drives or the parallel port for 1570 and 1571 drives.

You need the following parts to build this cable:

  • One solderable 6-pin male DIN plug (Commodore serial plug)
  • One solderable 15-pin male plug (PC game plug)
  • One solderable 25-pin male plug (PC parallel plug)
  • Four 1N5819 or BAT85 diodes
  • A shielded 4-wire or unshielded 5-wire cable of, preferably at most, 2 meters
  • A shielded or unshielded 8-wire cable of, preferably at most, 2 meters

Step 1. Solder one end of the 5-wire cable onto the DIN plug.

Step 2. Solder those wires of the 5-wire cable, that don't go through a diode, on the other end of the cable onto the parallel plug. These include the following connections:

DIN plug Parallel plug
 2, GND  18-25, GND
 3, ATN  13, Select
 4, CLK  12, PaperEnd
 5, DATA  10, Ack
 6, RESET  11, Busy

Step 3. Build the diode bridges between the appropriate pins of the parallel plug. These include the following connections:

Parallel plug Parallel plug
 13, Select   1, Strobe
 12, PaperEnd  14, AutoFeed
 11, Busy  17, SelectIn
 10, Ack  16, Init

The cathodes should be pointing towards the pins in the right column of the table.

Step 4. Solder one end of the 8-wire cable onto the game plug.

Step 5. Solder the other end of the 8-wire cable onto the parallel plug. You should have the following connections:

Game plug Parallel plug
 1   2, Data 0
 2   3, Data 1
 3   4, Data 2
 4   5, Data 3
 5   6, Data 4
 6   7, Data 5
 7   8, Data 6
 8   9, Data 7
not connected  18-25, GND

Circuit diagram:

[XMP1541 cable combo]

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

Source: The Joe Forster-STA homepage

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