Check list

Is the station connected to the power supply

Are the participants available in the TCP/IP network

Can the station be reached via the PING command

Can the station be reached via TELNET

Are the station 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 correctly, both in the driver dialog and in the address properties of the variable

Did you use the right object type for the variable

Does the offset addressing of the variable match the one in the station

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