Rs 485 communication

I am communicating two Different PIC IC 18f4685 and 16f877a through SPI communication.
it is communicating well. 16f877a IC is in front Board. I want the remote application such that if I connect same front board to other place distance is about 500m. I want same application will be done in both the front board.
We are using 9Pin connector. and RS485 how I will use that give me simple example of program in micro c. and data how send and recieve

You connect an RS-485 transceiver IC to the UART pins of the both PIC and connect the RS485 ICs together. Other than that, you just use UART code...just keep in mind that it is not duplex, it is half-duplex communications (unless you use two pairs of RS-485 transceivers), one dedicated to data flow one way, and another one dedicated to data flow the other way.