Are you planning to use 2 or 4 wire RS485?

If you use 2 wire, TX and RX occur over the same pair of data cables so only one device can TX at a time and every other device will receive the data. So your data should be in the form of a packet with a start byte, address byte/s, data byte/s and some sort of checksum or error checking. It's then up to the receiving device to determine if that packet of data was destined for it and perform the appropriate response. It is commonly a good idea for an acknowledge to be TX so the initiating device knows the data was received and processed.

4 wire should use the same protocol but TX and RX can occur at the same time.

Tony