If communications between the Modbus RTU Communications enabler and the controller are unsuccessful, use the following checklist to help find where the problem exists.
Verify that the:
COM port is configured in the system.
Cable between the computer and the controller is correctly wired.
Baud rate and parity on the computer are consistent with those on the controller.
Controller's Modbus port is configured for RTU communications.
Slave address is correct.
Validating Modbus RTU Communications.