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R.I.P: Commodore parallel transfer cable

Womo's »parallel cable standard«

As you can see at the pictures of the previous page, I personally don't like the »standard« Commodore parallel cables with only 10 wires and connectors with only 10 pins. Instead I prefer flat cables similar to the cables known from the products from Roßmöller. Their Speeder systems like Turbo-Access or Turbo-Trans made use of flat cables with 20 or 26 wires. The advantage of this is, that the 10 data lines become »shielded« by 11 intermediate wires, who are grounded. This also reduces crosstalking between the data lines and you probably can use longer cables.

For the same reasons and because I wanted to have some additional lines, I always used flat cables and connectors with 26 wires or pins. With the additional lines I was able to switch different ROMs within the Floppy drives directly from the C64. Resetting each drive exclusively was also possible. The table below describes my cable standard and some changes to it from the old days until now. Currently Nicolas Welte and I are discussing some design changes for the use with his 6502-RAMROM, which I tested recently.

Flat cable
pin No.
Wiremount socket
pin No.
DB25
pin No.
first specification later specification new standard proposion
1 1 1 GND GND
2 2 14 Handshake Floppy→C64 (CA2→Flag) Handshake Floppy→C64
3 3 2 GND GND
4 4 15 Parallel data bit 0 Parallel data bit 0
5 5 3 GND reserved/free
6 6 16 Parallel data bit 1 Parallel data bit 1
7 7 4 GND reserved/free
8 8 17 Parallel data bit 2 Parallel data bit 2
9 9 5 GND reserved/free
10 10 18 Parallel data bit 3 Parallel data bit 3
11 11 6 GND GND
12 12 19 Parallel data bit 4 Parallel data bit 4
13 13 7 GND reserved/free
14 14 20 Parallel data bit 5 Parallel data bit 5
15 15 8 GND reserved/free
16 16 21 Parallel data bit 6 Parallel data bit 6
17 17 9 GND reserved/free
18 18 22 Parallel data bit 7 Parallel data bit 7
19 19 10 GND GND
20 20 23 Handshake C64→Floppy (PC→CB1) Handshake C64→Floppy
21 21 11 GND GND
22 22 24 Kernal/DOS ROM switch bit 0 Kernal/DOS ROM switch bit 0
23 23 12 reserved for Kernal/DOS ROM switch bit 1 Kernal/DOS ROM switch bit 1
24 24 25 signed as »RAM«, soldered to C64 mainboard, meaning of it unknown reserved/free
25 25 13 reserved for dedicated Floppy reset +5V from C64 reserved/free
26 26 n.a. GND GND/free for use with DB25 connectors
Flat cable
pin No.
Wiremount socket
pin No.
DB25
pin No.
first specification later specification new standard proposion

Discussion and »standardisation« progress

On my first proposion for the new cable standard, Nicolas told me that there aren't enough free lines to control his 6502-RAMROM with all the options he would like. He proposed to reuse some of the GND lines which are fixed in the table above.

I have to admit, that this is an option, because the switch frequency on the parallel data lines is not too high. And if the GND signals were replaced by more or less static signals, that control the RAM, ROM or Flash options of the 6502-RAMROM, the shielding would be as much effective as with GND connected lines.
The only constraint of such a configuration is, that any of the GND replacing lines must not be »open« or floating, but either fixed to high or low level.

The handshake lines on the other hand must be surrounded by two GND signals, because short pulses of lengths of 1µs are sent over these two lines. In summary between 5 and 7 lines should be used for GND connections.

The following table shows current proposions out of our discussions and tracks down the usage of each line with different application scenarios. Bold printed entries denote fixed wires, that I don't wish to be changed because of the constraints above (and personal reasons).

Flat cable
pin No.
Wiremount socket
pin No.
DB25
pin No.
2003-03-13
migrate version
2003-03-13
alternative version
2003-03-13
no 6502-RAMROM use
1 1 1 GND
2 2 14 Handshake Floppy→C64 (CA2→Flag)
3 3 2 GND
4 4 15 Parallel data bit 0
5 5 3 6502-RAMROM:
ROM enable
6502-RAMROM:
main ROM, bit 0
Pull-down 4,7kΩ, both sides
6 6 16 Parallel data bit 1
7 7 4 6502-RAMROM:
RAM config, bit 0
6502-RAMROM:
RAM config, bit 0
Pull-down 4,7kΩ, both sides
8 8 17 Parallel data bit 2
9 9 5 6502-RAMROM:
RAM config, bit 1
6502-RAMROM:
RAM config, bit 1
Pull-down 4,7kΩ, both sides
10 10 18 Parallel data bit 3
11 11 6 GND
12 12 19 Parallel data bit 4
13 13 7 6502-RAMROM:
option ROM, bit 0
6502-RAMROM:
option ROM, bit 0
Pull-down 4,7kΩ, both sides
14 14 20 Parallel data bit 5
15 15 8 6502-RAMROM:
option ROM, bit 1
6502-RAMROM:
option ROM, bit 1
Pull-down 4,7kΩ, both sides
16 16 21 Parallel data bit 6
17 17 9 6502-RAMROM:
Flash write enable
6502-RAMROM:
main ROM, bit 1
Pull-down 4,7kΩ, both sides
18 18 22 Parallel data bit 7
19 19 10 GND
20 20 23 Handshake C64→Floppy (PC→CB1)
21 21 11 GND
22 22 24 Kernal/DOS ROM switch bit 0
6502-RAMROM: main ROM, bit 0
Kernal/DOS ROM switch bit 0
6502-RAMROM: ROM enable
23 23 12 Kernal/DOS ROM switch bit 1
6502-RAMROM: main ROM, bit 1
24 24 25 RAM enable, 6502-RAMROM:
not used with latest GAL
RAM enable
6502-RAMROM:
Flash write enable
25 25 13 reserved/application specific (e.g.: dedicated Floppy reset or +5V from C64)
26 26 n.a. GND/free for use with DB25 connectors
Flat cable
pin No.
Wiremount socket
pin No.
DB25
pin No.
2003-03-13
migrate version
2003-03-13
alternative version
2003-03-13
no 6502-RAMROM use
 

Wolfgang Moser, 2003-05-25,  ,  ("contact me" form disabled due to too high demand, sorry)