Sub OpenComPort()

Try

' Get the selected COM port's name 
' from the combo box.

If Not myComPort.IsOpen Then
myComPort.PortName = _
cmbPorts.SelectedItem.ToString

' Get the selected bit rate from the combo box.

If cmbBitRate.SelectedIndex > 0 Then
myComPort.BaudRate = _
CInt(cmbBitRate.SelectedItem)
End If

' Set other port parameters.

myComPort.Parity = Parity.None
myComPort.DataBits = 8
myComPort.StopBits = StopBits.One
myComPort.Handshake = Handshake.None

myComPort.ReadTimeout = 3000
myComPort.WriteTimeout = 5000

' Open the port.

myComPort.Open()

End If

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

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

Catch ex As System.IO.IOException
MessageBox.Show(ex.Message)

End Try

End Sub

Listing 2. Before transferring data, the application must set port parameters 
and open a connection to the port.