That exactly was the idea that had implemented long ago using standard UTP cable and distributing power through the free pairs to the slave devices. My setup had 1 master and up to 4 slaves at very slow speeds. But when all 4 slaves were connected, one was loosing communication from time to time. I have not found why up to this moment.

I am suspecting that the bus is at 3-state when no device is active and this is producing an error.

I used the ADM483EAR chip instead of SN75176 because of the fail safe protection. On a recent system I returned to the good old 176 and everything is cool. I added external resistor for the fail safe protection though.

Ioannis