Check list

Is the PLC connected to the power supply

Are the PLC and the PLC connected with the right cable

Did you select the right COM port

Do the communication parameters match (Baud rate, parity, start/stop bits,...)

Is the COM port blocked by another application?

Did you configure the Net address in the address properties of the variable correctly?

Did you use the right object type for the variable?

Does the offset addressing of the variable match the one in the PLC?

Are there terminators at the S485 bus system?

Use the DiagViewer for further analysis -> Which messages does it show?