so in etwa

Code:
Dim RS232 As New System.IO.Ports.SerialPort()

RS232.Open()

'#### Ein paar einstellungen vornehmen... ###
RS232.PortName = aComPort
RS232.BaudRate = aBaudRate
RS232.Parity = aParity
RS232.DataBits = aDataBits
RS232.StopBits = aStopBits
RS232.Handshake = aHandshake
RS232.RtsEnable = RTSenable
RS232.DtrEnable = DTRenable
RS232.ReceivedBytesThreshold = aReceivedBytesThreshold

        If RS232.IsOpen = True Then
            Debug.WriteLine("open   ")
            If RS232.BytesToRead() > 0 Then
                Debug.WriteLine("receiving")
                Messagebox.show(RS232.ReadExisting());
            Else
                Debug.WriteLine("nothing to read")
            End If
        Else