We used your 132 sets of RS485 access control boards, using two FC-08 converters, divided into two buses, the first has 103 access control boards, the second has 29, when connecting for communication, it was found that 29 devices on the second bus could not communicate, there is a communication indicator light next to the communication ports of all boards, it is different from the normal time, what is the problem?

Hello, if the communication indicator RX light is always on, it means that your RS485 is connected to A and B incorrectly, that is to say, the A of a device in your bus is connected to B, and B is connected to A, which is wrong. Please check the line to find the wrong device and connect it back in the correct way.

The following provides a set of error exclusion tables for reference