I have been tasked to design a serial card that can operate use RS232, RS422, and RS485. I found a transceiver (MAX3160) that can convert all three to signals my UART (TL16C554A) can handle. I started to worry about isolation to protect the system the card is in and also to eliminate any ground loops that can exist between my system and other systems so I began to look for an opto coupler for each serial channel. Because RS232, and RS422 use different voltage levels, I am having an issue locating an opto coupler that can handle either 232, or 422 depending on a jumper setting. Do I need to worry about opto coupling before the MAX3160 or can I do it after where all the levels are identical regardless of what serial standard I use. I would still want to optically isolate the signal ground at the connect however. Is this correct?
Thanks for any help.