Hi, coming back after the RS485 bus has been setup. Going on investigating about possible problems, we've found that we're defenseless against transmitters collisions: if a slave get stuck in transmitter mode (DE=1 in SN75176) when the master take the bus control, we have a fault on the line.
So I made up a test board with two transceivers: the first one fixed on transmission mode (DE=1 and D=0) and the second one with DE pin switchable between 0 and 1. When DE == 0 there's no problem and the supply current is about5mA. When we switch DE=1 supply current step up to 200mA.
We're trying a dominant/recessive scheme, based on DS36277 used in J1708 bus.