We have a design that does exactly that. We use a dual BAT54 schottky
diode, so speed is good and the voltage drop causes no problems.  The
common goes to the RX pin with a 5.1K pullup to VDD. Then the MAX232 inputs
drive each diode low coming out of the RS485 transceiver. We've gone to
250Kb without problems (DX512). One leg drives every few seconds, and the
other is an alternate.

--Bob

At 08:31 AM 6/19/2003 -0700, you wrote:
>I would like to have two RS232 devices share one serial port.
>
>I can make sure that only one device is active (sending) at a time. But
>can this be done electrically? Maybe some diodes or something?
>
>Thanks
>
>John
>
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