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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
|
|