I have long been familiar with RS-485 wired as a single differential pair connected to all the devices and termination at the both ends, however "end" may be defined. I have recently been looking into a 4- wire "full-duplex" implementation. However, it seems to be full- duplex only if there are only two devices attached. Otherwise, there appears to be a need to designate one device as the master (the device to whose receiver all the other drivers are connected) and the rest as slaves.
Unless there is some clever arrangement of which I am ignorant. Any comments?