Dim WithEvents BGW As New System.ComponentModel.BackgroundWorker With _
  {.WorkerReportsProgress = True, .WorkerSupportsCancellation = True}           _
   ' BackgroundWorker deklarieren
 
 Private Sub verbinden_Click(ByVal sender As System.Object, ByVal e As _
   System.EventArgs) Handles verbinden.Click
        With SerialPort1
            If verbinden.Text = "Verbinden" Then
                If Not .IsOpen Then
                    Try
                        .PortName = ComboBox1.Text
                        .BaudRate = 38400
                        .DataBits = 8
                        .Parity = Parity.None
                        .StopBits = StopBits.One
                        .WriteTimeout = 1000             ' 1000 ms = 1 Sek.
                        '.ReadTimeout = 1000             ' 1000 ms = 1 Sek.
                        .Open()
                    Catch ex As Exception
                        MessageBox.Show(ex.Message, "Fehler beim Open", _
                          MessageBoxButtons.OK, MessageBoxIcon.Error)
                        Exit Sub
                    End Try
                End If
                If Not BGW.IsBusy Then      'wenn BackgroundWorker aus -> Starten
                    BGW.RunWorkerAsync(SerialPort1)
                End If
                verbinden.BackColor = Color.Green
                verbinden.Text = "Verbunden"
            Else    'Verbindung abbrechen
                If BGW.IsBusy Then      'wenn BackgroundWorker an
                    BGW.CancelAsync()   'BackgroundWorker abbrechen
                End If
                verbinden.BackColor = Color.Red
                verbinden.Text = "Verbinden"
            End If
        End With
    End Sub
 
 Private Sub BGW_DoWork(sender As Object, e As _
   System.ComponentModel.DoWorkEventArgs) Handles BGW.DoWork
        'SerialPort lesen
        Do
            ' 7 Bytes Head lesen
            Dim head_array As Byte() = New Byte(6) {}
            Dim headBytesRead As Integer = 0
 
            While headBytesRead < head_array.Length
                Dim read As Integer = e.Argument.Read(head_array, _
                  headBytesRead, (head_array.Length - headBytesRead))
                headBytesRead += read
                If BGW.CancellationPending Then         'BackgroundWorker 
                ' abbrechen
                    Exit Do
                End If
            End While
 
            If head_array(0) = &HFF And head_array(1) = &H30 And head_array(2) _
              = &H1 Then
                Dim parameterlänge As Integer = (head_array(4) * 255) + _
                head_array(5) + 1
                Dim body_array As Byte() = New Byte(parameterlänge - 1) {}
                Dim bodyBytesRead As Integer = 0
 
                While bodyBytesRead < parameterlänge
                    Dim read As Integer = e.Argument.Read(body_array, _
                      bodyBytesRead, parameterlänge - bodyBytesRead)
                    bodyBytesRead += read
                    If BGW.CancellationPending Then         'BackgroundWorker 
                    ' abbrechen
                        Exit Do
                    End If
                End While
                If Checksumme(head_array, body_array) = False Then
                    MsgBox("nicht ok")
                    e.Argument.DiscardInBuffer()
                Else
                    'Daten an Form geben
                    BGW.ReportProgress(Nothing, New BGWUserState With _
                      {.BGW_head_array = head_array, .BGW_body_array = _
                      body_array})
                End If
            Else
                e.Argument.DiscardInBuffer()
            End If
        Loop
    End Sub
 
Class BGWUserState
        Public BGW_head_array() As Byte
        Public BGW_body_array() As Byte
 End Class
 
    Private Sub BGW_ProgressChanged(sender As Object, e As _
      System.ComponentModel.ProgressChangedEventArgs) Handles _
      BGW.ProgressChanged
        Dim UserState As BGWUserState = DirectCast(e.UserState, BGWUserState)
        If UserState.BGW_head_array(0) = 255 Then
            empfänger += 1
            TextBox1.Text = empfänger
        End If
    End Sub
 
    Private Sub BGW_RunWorkerCompleted(sender As Object, e As _
      System.ComponentModel.RunWorkerCompletedEventArgs) Handles _
      BGW.RunWorkerCompleted
        SerialPort1.DiscardInBuffer()
        SerialPort1.Close()
        ' MsgBox("BGW abgebrochen")
    End Sub
 
Function Checksumme(ByVal Hader_Daten As Array, ByVal Body_Daten As Array) As _
  Boolean
       ... 
End Function