Hello,

I am currently using an S7-1500 PLC with the 6ES7 137-6AA01-0BA0 CMPtP module to communicate with a device via RS-485 using MODBUS. I have encountered synchronization errors when trying to communicate, and I would appreciate your help in troubleshooting this issue.

Setup:

• PLC:S7-1500
• Communication Module:6ES7 137-6AA01-0BA0 CMPtP (configured for 2-wire RS-485)
• MODBUS Protocol:Using Modbus Master block to read 4 subsequent registers from a single connected device.
• Instance DB Mode:Mode 4 in MB_COMM_LOAD instance DB.

Issue:

When trying to read from the MODBUS device, I receive the following synchronization errors:

• 16#81E7
• 17#81E2

Interestingly, the setup was working fine previously, but now, after replacing the communication module with an identical one (same order number), it starts giving the errors mentioned above.

However, when I replace the problematic module with another one of the same type, the communication works as expected.

Questions:

1. What could cause these synchronization errors with the module even though everything was working correctly before?
2. Is there any specific configuration or hardware issue that might be affecting the communication with this module?
3. Could the error be related to the module’s firmware, or is it likely a configuration issue on the PLC or the communication setup?
   

Any help or suggestions would be greatly appreciated. Thanks in advance!

attached screenshots of configuration