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SpeedDOS Cable (parallel floppy speeder cable)

Project: Cable for parallel data transfer.
Target : C64 + 1541
Time   : 25 min.
Cost   : <10 US$
Use    : Speed up for floppy operations


Cable which connects to the C-64's user port and to the 1541's VIA #1.


Since port A of the VIA #1 in UC3 (old 1541) in the 1541 is free, it can be used to transfer data to the user port, 8 bits at a time, which is 8 times as much as with the 1-bit serial bus. You need either programs that make use of this cable, or a parallel speeder, like SpeedDOS, Dolphin DOS 2.0, TurboTrans, etc.

Note that if you want to use such a cable with a 1541c, you need to exchange its ROM. At least that's the theory, I haven't tested it yet.



  1. The parallel cable connects the user port with the drive's yet unused internal VIA port according to the following scheme:

           User port    | VIA in UC3 (old 1541, read notes below)
           B (/Flag2)   | 39 (CA2)    
           C (PB0)      |  2 (PA0)
           D (PB1)      |  3 (PA1)
           E (PB2)      |  4 (PA2)
           F (PB3)      |  5 (PA3)
           H (PB4)      |  6 (PA4)
           J (PB5)      |  7 (PA5)
           K (PB6)      |  8 (PA6)
           L (PB7)      |  9 (PA7)
           8 (/PC2)     | 18 (CB1)
           A (GND)      |  1 (GND)

  2. Solder the user port connector to the Vector board and make the appropriate connections to the multipin connector according to the cable you used (10- or 20-pin).
  3. After you disconnecting the floppy drive, open the drive's case. In case the VIA in UC3 is not socketed, either solder the cable directly to the VIA's pins or, if you are more experienced, remove the VIA and solder a high precision IC socket in UC3.
    Now solder the flat cable according to the scheme above to the second IC socket. Insert the 'cable socket' into the PCB socket and then the VIA into the 'cable socket'.
  4. Plug in the parallel cable (your equipment must be still switched off!), power on both C64 and 1541, and test the cable using a parallel copy program like FCOPY III, or if you have SpeedDOS, check if it loads faster now.
  5. If everything seems fine, close the case again.

Possible failures

Updated: January 13th, 1999
Created: January 1997
Status : Partially verified on November 5th, 1997

Site copyright © 1997 by Marc-Jano Knopp
This document is part of MJK's Commodore 64 & LCD Page
Brought back to life by Peter Schepers, Dec 10, 2005 because I really liked this site!