Possible reasons for no output or output errors

1. The computer has a COM port, but the selected port is incorrect.

2. TTL to 485 module operation/programming toggle switch selection is incorrect.

3. Wrong baud rate.

4. The 485 bus is disconnected, or the A and B lines are connected reversely.

5. If there are too many devices or the wiring is too long, power supply should be provided nearby.

Equipment damage.