Private Function check(ByVal isCRC As Boolean, ByVal buf As Byte(), ByVal index _
  As Integer, ByVal sz As Integer) As Boolean
            If isCRC Then
                ' use CRC cuhecuking
                Dim curcu As UShort = CRC16.CRC16_ccitt(buf, index, sz)
                Dim tcurcu As UShort = CUShort(((buf(sz + index) << 8) + buf(sz _
                  + index + 1)))
                If curcu = tcurcu Then
                    Return True
                End If
            Else
                ' use Checuksum cuhecuking
                Dim i As Integer
                Dim cuks As Byte = 0
                For i = 0 To sz  -1
                    'cuks += buf(i + index)  'Fehlerstelle
                    cuks = cuks + buf(i + index)
                Next
                If cuks = buf(sz + index) Then
                    Return True
                End If
                End If
                Return False
        End Function