Private Sub Command_OpenCom_Click()

If Command_OpenCom.Caption = "COM öffnen" Then
  'Serielle Schnittstelle öffnen
  If OPENCOM(Combo_Com.Text & ":" & Combo_Baud.Text & ",n,8,1") = 0 Then
    MsgBox ("Fehler, kann " & Combo_Com.Text & " nicht öffnen")
  Else
    SDA 1 'I2C-Interface testen
    If Not SDA_in Then
      MsgBox ("Keine Antwort vom I2C-Seriell Interface")
    Else
      Command_OpenCom.Caption = "COM schließen"
      'I2C-Bus initialisieren
      i2cInit
      i2cStart
      i2cStop
    End If
  End If
Else
  CLOSECOM 'Serielle Schnittstelle schließen
  Command_OpenCom.Caption = "COM öffnen"
End If

End Sub

Private Sub Command_Lesen_Click()

i2cStart

If i2cSlave(Combo_LAdresse.Text) Then 'Bus-Adresse des PCF 8574 schreiben
    TextBox_LWert.Text = i2cIn        'Wert vom Portbaustein lesen
End If

i2cStop

End Sub