Hello everyone,

My name is Sam, and I am currently working on a project involving two Beckhoff CX9020-0115 PLCs. Both PLCs are equipped with a Modbus TCP/IP license. I’m trying to perform a communication test where:

And the library that I used is TF6310.

• PLC1 (IP: 169.254.232.100) is configured as the Modbus TCP Master
• PLC2 (IP: 169.254.232.101) is configured as the Modbus TCP Slave

I have written the Structured Text (ST) code for the master side and attempted to run both PLCs online (using TwinCAT 3 on two different projects). However, I am not receiving any data from the slave side, and I’m unsure where the issue lies—whether on the master or slave configuration/code.

Has anyone here successfully set up Modbus TCP communication between two CX9020 PLCs before? I’d really appreciate if someone could share insights, example code, or even just tips on what to double-check (e.g., mapping, ports, enabling server, etc.).

Any help would be highly appreciated.

Best regards,
Sam