Nota : A maioria dos computadores atuais não tem mais portas seriais.
Esta tarefa foi transferida para as portas USB.

Module PortaSerial

    Sub SendSerialData(ByVal data As String)
        ' Send strings to a serial port.
        Using com1 As IO.Ports.SerialPort = My.Computer.Ports.OpenSerialPort("COM4")
            If com1.IsOpen Then
                com1.BaudRate = "9600"
                com1.DataBits = 8
                com1.Parity = 0
                com1.StopBits = 1
                com1.WriteLine(data)
            Else
                MsgBox("A porta está fechada.")
            End If
            com1.Close()
        End Using
    End Sub

    Private Sub ReceiveSerialData()

        ' Receive strings from a serial port.
        Dim returnStr As String = ""
        Dim Incoming As String

        Dim com1 As IO.Ports.SerialPort = Nothing
        Try
            com1 = My.Computer.Ports.OpenSerialPort("COM4")
            com1.BaudRate = "9600"
            com1.DataBits = 8
            com1.Parity = 0
            com1.StopBits = 1
            com1.ReadTimeout = 1000 '1seg
            Do
                Incoming = com1.ReadLine()
                If Incoming Is Nothing Then
                    Exit Do
                Else
                    returnStr &= Incoming & vbCrLf
                End If
            Loop
        Catch ex As TimeoutException
            returnStr = "Erro: Time out na leitura da porta Serial."
        Finally
            If com1 IsNot Nothing Then com1.Close()
        End Try
        MsgBox(returnStr)
    End Sub

End Module