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I think you are confusing the signal requirements on the RS485 side and the micro-controller side. The RS485 side can handle voltages in excess of Vcc. See data sheet. (Common mode range: -7V to...
Art and Science of RS485 from Circuit Cellar Ink magazine way back in 1999 is always a good thing to read when starting out with RS485. Google usually turns up a link or two to a copy.
Some of the MAXIM chips have slightly altered input...