Hello,

should be ok, in other case swap A and B wires can be made. How to detect if your module is damaged is not quickly made, some more tests need to be done. Maybe first check online your HW for some problems, diagnostic buffer. Generally some communication tests can be initiated with PC sim SW and your PLC but correct wiring play role here also. Also some not exactly Modbus but otgher type of protocols testing you can make, here you can also test cfg of module comm parameters via code. More different tests, better know about functionality.