I have the wiring diagram for SUB D9 **broken link removed**
This is for a 80ft run. I thought it was better to twisted cable which I have.So which is better straight or twisted pair?
If twisted pair will work which connections?
Thanks
If you are intending to run this link at higher speeds (9600bps or greater) you may have problems with reliable data transfer.
RS232 is not balanced in any way, using twisted cable is unlikely to improve anything, depending on which signals are "twisted together" this could increase the unwanted stray coupling in a long cable run.
80ft for a null modem cable !!! ...are you serious..
RS 232 is not designed for long distance communications, use RS 485 instead. RS 485 uses three lines, two of which are differentially balanced and the third is the ground. Most RS485 networks run in half-duplex mode.
With RS485 you can go upto 4000 feet..See EIA-485 - Wikipedia, the free encyclopedia for general information. The RS232 port of the computer can be converted to RS485 signalling standard using a converter such as the SN75176.
You could also use a standard RS232 to RS485 converters.
Google for more information on RS485, there are many projects/solutions in the internet.
Running at a low speed, say 300bps, it may work OK, but without knowing the application, that may not be appropriate and RS232/485 converters would be a good way to go, and he could use the twin twisted cable no problem.
Can I add that it would probably be better to use RS422 rather than RS485.
RS422 will allow full duplex communication and uses two pairs of wires, whereas RS485 will only allow half duplex and will need flow control to switch the 232/485 converters.
Back when I was in collage we ran RS232 for lengths far in excess of the spec. I recall most worked well at 9600 but not 19200. This was from a pdp 11/45 to mostly Heath H19 terminals.
My guess is that most of these were over 80 feet. The computer was up on floor and halfway across the building from the offices.
Having said that I doubt anyone would go that route today.