Been a while since I asked this question originaly, but now I have to
actually do the connections.

I am a little confused on the placement of the diodes. Can they be placed
before the level shifter on the transmitting serial lines(+/-12V),  or do
they have to go after the level shifter(0-5V)? I am hoping there is a way
that two transmitting serial lines can be connected to one channel on the
level shifter, otherwise I will have to change my level shifter for more
channels.

Thanks

John


----- Original Message -----
From: "Bob Axtell" <cr_axtell@YAHOO.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, June 19, 2003 9:32 AM
Subject: Re: [PIC] 2 - RS232 lines into 1 serial port?


> 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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