Nigel, thank you for your answer.  Are there 3V chips that include "or" and
"and" gates?

Also, I think I should be switching the AND gates and thr OR gates,
shouldn't I?  I should feed the input to AND gate with the other input of
each AND gate going to separate PIC pins.  Feed the two outputs of the AND
gates into an OR, the output of the OR goes into the PIC USART pin.

-----Original Message-----
From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU] On
Behalf Of Nigel Orr
Sent: Thursday, April 22, 2004 2:21 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PICLIST] [EE]: 2 RS232 connections on 1 RS232 port

You can put each TTL level comms line into one input of an OR gate, with
the other input of each OR gate going to separate PIC pins.  Feed the two
outputs of the OR gates into an AND, the output of the AND goes into the
PIC USART pin.

If either of the control lines is low, that port's data will pass through
to the PIC.  (TTL level serial comms idles high)

That's the basic idea, you could reduce it to one control pin from the PIC
without much extra logic

Nigel

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