Private Sub SendCommand(ByVal command As String)

Dim response As String

Try

myComPort.WriteLine(command)
response = myComPort.ReadLine

Select Case response

Case "0"
lblStatus.Text = "LED 1 is OFF"

Case "1"
lblStatus.Text = "LED 1 is ON"

Case Else

End Select

Catch ex As TimeoutException
MessageBox.Show(ex.Message)

Catch ex As InvalidOperationException
MessageBox.Show(ex.Message)

Catch ex As UnauthorizedAccessException
MessageBox.Show(ex.Message)

End Try

End Sub

Listing 4. The SendCommand routine sends a text command 
to the COM port and waits for a response.