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.
On circuit diagrams, plugs are displayed as viewed from the back side, the solder side. Chips are displayed as viewed from above; also, see the small semicircular cut for finding the correct orientation. When in doubt, see the corresponding description on the legend page.
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)
Eight diodes (e.g. 1N4148)
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 the other end of the 5-wire cable onto the parallel plug. These include the following connections:
|DIN plug|| Parallel plug |
|2, GND||18-25, GND |
|3, ATN|| 1, Strobe |
|4, CLK|| 14, AutoFeed|
|5, DATA|| 17, SelectIn|
|6, RESET|| 16, Init |
Step 3. Solder one end of the 8-wire cable onto the game plug.
Step 4. Solder those wires of the 8-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:
|Game plug|| Parallel plug |
|1|| 13, Select |
|2|| 12, PaperEnd|
|3|| 10, Ack |
|4|| 11, Busy |
|not connected||18-25, GND |
Step 5. Solder the remaining wires of the 8-wire cable through a diode onto the parallel plug. These including the following connections:
|Game plug|| Parallel plug |
|5|| 6, Data 4 |
|6|| 7, Data 5 |
|7|| 8, Data 6 |
|8|| 9, Data 7 |
The cathodes of the diodes should be pointing towards the pins in the right column of the table.
Step 6. Build the diode bridges between the appropriate pins of the parallel plug. These include the following connections:
|Parallel plug|| Parallel plug |
|10, Ack|| 4, Data 2 |
|11, Busy|| 5, Data 3 |
|12, PaperEnd|| 3, Data 1 |
|13, Select|| 2, Data 0 |
The cathodes should be pointing towards the pins in the right column of the table.
You can find the description of all parts used on the diagrams at the legend page.
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