MSComm32 and SComm32 have the same syntax and functionality
value = SComm1.DSRHolding
A Boolean Expression indicating the current state of the DSR line.
If SComm1.DSRHolding = True Then
MessageBox.Show("DSR is On")
MessageBox.Show("DSR is Off")
When connecting two devices, computers etc via their RS232 ports the DSR on one device is usually connected to the DTR on the other. When a remote device is powered up and ready to communicate it usually sets its DTR line ON which would be detected by the remote device as a change in the state of its DSR line.