Ecoli-557, I use RS-485 for communications with 5 dual axis tracking solar arrays. As Henrik has mentioned in his first sentence, Half duplex RS-485 should have a master to solicit the communications. That way you dont loose data to collisions. If the structure were full duplex,(4 wire) then you could have the slave units request data from the master or even other slaves. This type of communications can be done with half duplex but, you need to seriously think about the protocol to be used.