Re: Splitting serial cables ?


<briggs@xxxxxxxxxxxxxxxxx> wrote in message
news:oCgSttFou3DR@xxxxxxxxxxxxxxxxxxxxxxxxxxx
> In article <43DD3DBC.6E32BF1E@xxxxxxxxxxxx>, JF Mezei
> <jfmezei.spamnot@xxxxxxxxxxxx> writes:
[...snip...]
>
> Transmit data is on one of those wires. You have two stations both
> wired into transmit data. Both of them will be holding that lead
> in the space condition (or mark -- I can never remember) when idle.
> This is not tri-state logic where the lead floats when idle.
>
> If you've ever put a breakout box on an RS232 connector, you'll have
> noticed that TD and RD are always live.
>
[...snip...]
>
> You can have one source sending data to multiple receivers. That's
> no problem since the receivers aren't trying to coerce the signal line.
>
> You can't have multiple sources sending data to a single receiver.
> That's a problem since multiple senders are each trying to coerce
> the signal line differently.
>
Umm, if you read my original post you'll notice that I said 2 diodes were
required to isolate the two transmit lines from each other. Only one phase
of the signal (negative if memory serves) is required to send data from
transmitter to receiver. Without the diodes one transmitter would be
positive while the other is negative and you would have a problem.

Neil Rieck
Kitchener/Waterloo/Cambridge,
Ontario, Canada.
http://www3.sympatico.ca/n.rieck/links/cool_openvms.html


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