The RS485 network does not need a "supply". But for long distance it is prefered to use two 560 Ohm resistor to pull the "+" signal line to +9V and "-" signal line to 0V to give the RS485 bus a "bias" voltage. You may be able to use the 5V analog reference as a high bias on the master node although a +9V supply will be better. Do not put multiple biasing on the RS485. Just on one or two ends of the RS485 bus will do.
