① First check the main controller baud rate, parity bit, address, etc., whether the settings are correct;
② Confirm whether the communication wire used is standard, 485 twisted pair shielded wire;
③ Confirm whether there is a virtual connection between the communication line and the host "A, B" terminal and rail voltage terminal, etc.;
④ Use a multimeter to measure whether there is an output voltage on the "A, B" terminals on the host module. The normal output voltage is between 3v-5v; Note: (When measuring, first remove the communication line and tighten the screws)
⑤ If the output voltage of the "A, B" terminals is normal, it may be a communication line failure, or there may be a problem with the back-end system, and you should find the corresponding manufacturer for processing;
⑥ If there is no output voltage at the "A, B" terminals, the module is broken.
