Hello, we have purchased 132 sets access controller of RS485 Communication way from your company, use two FC-08 converter and separate with 2 wires, the first wire has 103sets access controllers, the second wire has 29 sets, when connected them, we found the second wire communication failure, it has a communication indicator normal light which behind all boards, is not the same as the normal time, what’s wrong of that?

If communication indicator RX light is always opened, that means it has one device connect opposite with A and B in RS485 wire. Please check the circuit to find out the wrong device and connect it in correct way.