Cable Specification for Direct-Cable Connection

by Johannes Helmig [Published on 14 Feb. 2000 / Last Updated on 14 Feb. 2000]

If you have the proper tools and intend to "manufacture" your own serial or parallel DCC cable,
or if you like to check a purchased cable, then this page is for you.

Without proper tools, I strongly suggest that you purchase a High Speed DCC cable.


If you have decided to make your own cable :
You may make a mistake , so the reminder that here is a DCC Trouble-Shooting page
and that you can test / troubleshoot your Parallel DCC connection using a great
utility from Parallel Technologies calledDirectParallel® Connection Monitor



When it comes to cables, I have a rule:
" Do NOT trust any cable, which you either made yourself or tested yourself !"
The Microsoft "Windows95 Resource-Kit" informed about DCC cables
(which is partially not correct, see below):

The above information in the Microsoft "Windows95 Resource-Kit" about DCC cables:
"Cables Compatible with Direct Cable Connection" is partially wrong:
- There is no ECP Cable !
- The Universal Cable Module (UCM) is called DirectParallel Universal Fast Cable ...


Serial cable:

Be care: DCC requires for Serial connections a "real" NULL-Modem cable with ALL wires, where you can have either a 9-pin(DB9) or 25-pin(DB25) serial connection. This information is according to the Microsoft Knowledge Base
article Q142324 and a TechNet article Appendix B - RAS Cabling:

Signal: 9-Pin 25-pin 25-pin 9-pin Signal
Ground 5 7 <- the ONLY not crossed wire-> 7 5 Ground
Transmit 3 2 <----> 3 2 Receive
Receive 2 3 <----> 2 3 Transmit
RTS 7 4 <----> 5 8 CTS
DSR,CD 1,6 6,8 <----> 20 4 DTR
CTS 8 5 <----> 4 7 RTS
DTR 4 20 <----> 6,8 6,1 DSR,CD

Note the connections between pins 1+6 for the 9-pin connector
and between pins 6+8 for the 25-pin connector.

Quote from the TechNet article:
"Off-the-shelf null modem cables might be improperly wired.
Be sure to tell your dealer that your null modem cables must be wired
as shown in table ..."



But also the following cable WITHOUT the connections between the pins
has worked for me (no guarentee that it will also work for you):

Signal: 9-Pin 25-pin 25-pin 9-pin Signal
Ground 5 7 <- the ONLY not crossed wire-> 7 5 Ground
Transmit 3 2 <----> 3 2 Receive
Receive 2 3 <----> 2 3 Transmit
RTS 7 4 <----> 5 8 CTS
DSR 6 6 <----> 20 4 DTR
CTS 8 5 <----> 4 7 RTS
DTR 4 20 <----> 6 6 DSR


And also the following cable, which I purchased and then measured, has worked:

Signal: 9-Pin 9-pin Signal
Ground 5 <- the ONLY not crossed wire-> 5 Ground
Transmit 3 <----> 2 Receive
Receive 2 <----> 3 Transmit
DTR 4 <----> 6 DSR
DSR 6 <----> 4 DTR
CD 1 (??) <----> 7 RTS
RTS 7 <----> 1 (??) CD



Parallel Cable:

I found recently in the Computer journal "PC Professional" (German version of "PC-Magazine") in Nov.97 on page 286 the following wiring for a parallel DCC cable (which I did not test myself, so do NOT blame me if it does NOT work),
also listed now in Q142324 and TechNet article Appendix B - RAS Cabling::

Signal: 25-Pin 25-Pin Signal
bit 0 2 <----> 15 Error
bit 1 3 <----> 13 Selected
bit 2 4 <----> 12 Paper out
bit 3 5 <----> 10 Ackn.
bit 4 6 <----> 11 Busy
Error 15 <----> 2 bit 0
Selected 13 <----> 3 bit 1
Paper out 12 <----> 4 bit 2
Ackn. 10 <----> 5 bit 3
Busy 11 <----> 6 bit 4
Ground 25 <----> 25 Ground

Such a parallel cable is sometomes called "parallel LapLink cable" or "parallel InterLink cable", and when I recently opened the box of Symantec pcAnywhere, it included such a parallel port cable.

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