What is the purpose of the MARK point identification signal in KM-ASSYM4-01?

What does the error message M7090-PLC mean?

What could be causing the host computer to time out waiting for the MARK point identification signal in KM-
The M7090-PLC error occurs when the host computer fails to transmit the MARK point identification signal within the specified timeline. To resolve this issue, first confirm that the host computer is correctly configured and sends the signal within the