Michael Watterson wrote:
>> Seems reasonable to me.  Just make sure that each signal (receive,
>> transmit) is on its own twisted pair with the other wire of the pair
>> being ground.  In other words, the minimum RX/TX lines will use up
>> half the CAT5 cable.
>>
> however many offices use 9,600 or 19,200 RS232 with only one earth
> wire
> and 4 or 6 signals over CAT5 structured wiring, so possibly up to
> 100m.

RS-232 is pretty forgiving and you can often get away with some sloppiness.
However, that doesn't make it a good idea, nor is a few instances of
something working proof of much.

> Olin's custom twisted pair scheme of ground on each half of each pair
> is only needed either for 115k or longer distance.

I don't know about "custom" since I didn't say anything about pinout.  You
can wire up the connectors to the ends of the CAT5 cable any way you want.
The OP didn't say anything about using pre-made standard ethernet cables,
only "CAT5".  In any case, RS-232 over CAT5 with RJ-45 connectors is pretty
unusual and there isn't much of a standard whether someone wrote something
down or not.

The longer the runs are and the faster the baud rate, the more you need to
clean about things.  It's impossible to come up with a universal limit of
how fast and how far before you need certain precautions.  Ground loops,
external noise, and EMI all make a difference.

Unless the OP needs the extra wires for something else he hasn't mentioned,
I'd go for maximum signal integrity.


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