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

Summary

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

Details

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.

Ingredients

~1m 10-core flat cable OR
~2m 20-core flat cable
1 user port connector
1 piece of Vector board, matching the user port connector's dimensions
1 2-row multipin connector and appropriate crimp plug, number of pins is the same as flat cable
1 40-pin high precision IC socket (if VIA is socketed) OR
2 40-pin high precision IC socket (if upgrading with socket)
For 1541c:
1541 or 1541-II ROM
Optionally:
SpeedDOS ROM images

Instructions

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)
     
```
Notes
- To safely find out which VIA is the one with the unused port, simply look at pins 2-9 of both the VIAs (6522) on both sides of the 1541 board and check if they are connected to anything (you don't even need a multimeter for this, just keep your eyes open).
- On the 1541-II, pin 2 of the VIA is grounded, just cut the trace between pin 1 and pin 2.
- On the 1541c, pin 2 is used for Track-1 detection (AFAIK). Cut the trace and exchange your drive's ROM with a standard 1541 or 1541-II ROM.
- The GND connection is not necessary for most of the parallel speeder/copy programs, since the serial cable supplies the GND line. For enhanced data safety, we recommend using a 20-pin flat cable, with each 2nd wire connected to GND. This even enables you to simply use a 20-pin multipoint connector which is crimped on the cable.
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).
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'.
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.
If everything seems fine, close the case again.

Possible failures

Soldering iron not plugged in

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