Hello everyone,

My work has a product that has four pins for RS232, RS485, or RS422.
Previously the product was built as either RS232 or RS485/RS422 - only
containing a transceiver for one or the other but not both. But now we
want to make a product that can be electronically configured as one or
the other. The problem is that the same pins are used for each
interface!

I was wondering if anybody has any suggestions for a circuit that
would permit the either of the transceivers (232 and 422) to be
disconnected from the circuit - so that only one was physically
connected to the pins at a time. Off the top of my head I can think of
two solutions:

(1) Signal relays on the input/output of each transceiver. This would
permit the 232/422/485 to be on the same pins.
Pros: Robust
Cons: bulky, power hungry, and expensive.

(2) Electronic switch, would a CD4066B work? An electronic switch is
desirable but many don't handle the voltages required. For instance
the MAX232 tolerates +/-30V whereas the seemingly obsolete CD4066B
only handles 0-15V, requiring protection.
Pros: Smaller
Cons: Not sure how to implement, inadequate voltage tolerance

--=20
Jason White
--=20
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