Modbus RTU and 750-653

How to use 750-653/003-000 module for modbus RTU (RS 485) communication in codesys 3.5?

CODESYS does not support using the Modbus configuration for a 750 module the same way it does for on-board ethernet and serial ports. You will need to use the WagoAppPlcModbus library. This contains a FbMbMasterSerial function block that you can use. Just use the name of the 750-653 module as the I_Port input of the function block.

Then add your desired Baudrate, Data Bits, etc to those inputs as well. You will have to manually manage the utQuery structure and xTrigger input to do the required operation on the Modbus servers you have attached.