AVR-Chat

If the transceiver is one that has the built-in offset so
that 0V is a properly defined logic state, then you just
terminate with the resistor between the A and B lines.

If you are using older transceivers with no offset, then
you need to pull one side high (with, maybe, a 4.7K) to the
local 5V and the other side down to local ground with the
same resitor size. Then, you add the termination resistor,
line to line. This provides a bit of bias to provide the
necessary undriven line state.

For good information about RS422 and 485, check

http://www.national.com/an/AN/AN-1031.pdf
http://www.national.com/an/AN/AN-409.pdf
http://www.national.com/an/AN/AN-409.pdf

Jim Wagner

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