I had been reading avrfreaks topics about this subject, but I still have some doubts about what I should use in a project I'm working on.
I'm going to describe it:
One central board(brain) and several other boards(user keypad) all connected in a network.
The brain talks to all boards, but the keypads only talk to the brain and not among them.
The brain can start talking to a keypad to make it beep, as well as the keypad can start talking with the brain to ask it some information to display.
So, all of them can act as master or slave.
Each board has an ATMega128 and I'm thinking in using RS485 as the network physical layer.
Can you advise me which protocol should I implement?
Modbus would be the perfect solutions if I hadn't the need for multi-master. On the other hand, SNAP allows multi-master but lacks collision avoidance.