You should follow these instructions if your drive has no parallel capabilities yet and you want to connect the cable directly onto the periphery chip in the drive. If possible, you shouldn't use this method because, this way, you won't be able to make use of it with a Commodore machine.

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. 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.

Construction

You need the following parts to build this cable:

• One solderable 25-pin male plug (PC parallel plug)

• Eight diodes (e.g. 1N4148)

• A shielded or unshielded 8-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 those wires, that don't go through a diode, on the other end of the cable onto the parallel plug. These include the following connections:

     VIA#1     
 Parallel plug 

     2, PA0    
   13, Select  

     3, PA1    
   12, PaperEnd

     4, PA2    
   10, Ack     

     5, PA3    
   11, Busy    

 not connected 
18-25, GND     

Step 3. Solder the remaining wires through a diode onto the parallel plug. These including the following connections:

     VIA#1     
 Parallel plug 

     6, PA4    
    6, Data 4  

     7, PA5    
    7, Data 5  

     8, PA6    
    8, Data 6  

     9, PA7    
    9, Data 7  

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

Step 4. 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.

Circuit diagram

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

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