> Has anyone out there used the 16C74a with an RS-485 2-wire network?  If so,
>  how is it any different than using RS232 (except for levels, of course).
Am
>  I required to use addressing?  Would I decode the addressing in software or
>  hardware?
>
Most significantly, RS485 is half duplex ... you need to control the Rx/Tx
mode of the buffer chip as well as the actual Rx & Tx signals (ie: three pins
from the PIC).
As to addressing or whatever ... totally dependant on what software protocol
you decide to write; typically you would have a master/slave type where all
devices except one are receiving, unless they receive a request for data from
the one master device.

Ian C.