'Einrichten der Com
Private Sub verbinden_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles verbinden.Click
        With SerialPort1
            If Not .IsOpen Then
                Try
                    .PortName = ComboBox1.Text
                    .BaudRate = 38400
                    .DataBits = 8
                    .Parity = Parity.None
                    .StopBits = StopBits.One
                    .WriteTimeout = 100                ' 1000 ms = 1 Sek.
                    .ReadTimeout = 100                 ' 1000 ms = 1 Sek.
                    .Open()
                    verbinden.BackColor = Color.Green
                    verbinden.Text = "Verbunden"
                Catch ex As Exception
                    MessageBox.Show(ex.Message, "Fehler beim Open", _
                      MessageBoxButtons.OK, MessageBoxIcon.Error)
                    Exit Sub
                End Try
            End If
        End With
    End Sub
 
...
Me.SerialPort1.ReceivedBytesThreshold = 1  'nach 1 Bytes DataReceived Event 
' auslösen
...
   Sub SerialPort1_DataReceived(ByVal sender As Object, ByVal e As _
     System.IO.Ports.SerialDataReceivedEventArgs) Handles _
     SerialPort1.DataReceived
        With SerialPort1
            Try
                Bufferbyte = .ReadByte
                Select bytezähler
                    Case 0
                        If Bufferbyte = &HFF Then  'Start
                            bytezähler = 1
                        End If
                    Case 1
                        If Bufferbyte = &H30 Then   'Version
                            bytezähler = 2
                        Else
                            bytezähler = 0
                        End If
                    Case 2
                        If Bufferbyte = &H1 Then    'Ziel
                            bytezähler = 3
                        Else
                            bytezähler = 0
                        End If
                    Case 3
                        quelle = Bufferbyte         'Quelle
                        bytezähler = 4
                    Case 4
                        anzahlpara = Bufferbyte * 255
                        bytezähler = 5
                    Case 5
                        anzahlpara = anzahlpara + Bufferbyte
                        bytezähler = 6
                        zahler = 0
                    Case 6
                        ByteArray(zähler) = Bufferbyte
                        zähler += 1
                        Debug.Print(zähler)
                        If zähler = anzahlpara - 1 Then
                            MsgBox("hallo")
                        End If
                End Select
 
            Catch ex As Exception
                MessageBox.Show(ex.Message, "Fehler beim Empfangen ComPort...")
                If SerialPort1.IsOpen Then .DiscardInBuffer()
            End Try
        End With
    End Sub

...
Me.SerialPort1.ReceivedBytesThreshold = 1  'nach 1 Bytes DataReceived Event 
' auslösen
...

Me.SerialPort1.ReceivedBytesThreshold >= 1

________
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Me.SerialPort1.ReceivedBytesThreshold = 7

Option Explicit On
Option Strict Off
Imports System.IO.Ports
Imports Microsoft.Win32
Imports Microsoft.VisualBasic
 
 
Public Class Form1
 
    Dim T3_IO_Status_Array(0 To 100) As Byte
    Dim ByteArray(0 To 100) As Byte
 
    Private Delegate Sub DelegateSub()
    Private Aktualisieren As New DelegateSub(AddressOf updateForm)
 
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) _
      Handles Me.Load
        'Com-Ports finden
        Dim EinzelPort As String
        For Each EinzelPort In My.Computer.Ports.SerialPortNames
            ComboBox1.Items.Add(EinzelPort)
        Next EinzelPort
 
    End Sub
    Private Sub verbinden_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles verbinden.Click
        With SerialPort1
            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.
                    .ReceivedBytesThreshold = 8
                    .Open()
                    verbinden.BackColor = Color.Green
                    verbinden.Text = "Verbunden"
                Catch ex As Exception
                    MessageBox.Show(ex.Message, "Fehler beim Open", _
                      MessageBoxButtons.OK, MessageBoxIcon.Error)
                    Exit Sub
                End Try
            End If
        End With
    End Sub
 
    Sub SerialPort1_DataReceived(ByVal sender As Object, ByVal e As _
      System.IO.Ports.SerialDataReceivedEventArgs) Handles _
      SerialPort1.DataReceived
        'System.Threading.Thread.Sleep(50)
        Delay(50)           'warten bis Telegramm empfangen ist
        If DatenPruefen() = True Then
            If ByteArray(1) = &H30 And ByteArray(2) = &H1 And ByteArray(6) = _
              &H66 Then   'Staus
                ByteArray.CopyTo(T3_IO_Status_Array, 0)  'Datenübertrag
                Me.Invoke(Aktualisieren)
            End If
        End If
    End Sub
 
    Function DatenPruefen() As Boolean
        DatenPruefen = False
        With SerialPort1
            Try
                Dim count As Integer = .BytesToRead  'Anzahl der empangenden 
                ' Byts
                .Read(ByteArray, 0, count)
                If ByteArray(0) = 255 And Checksumme(ByteArray) = True Then
                    DatenPruefen = True
                End If
                .DiscardInBuffer()
            Catch ex As Exception
                MessageBox.Show(ex.Message, "Fehler beim Empfangen" & _
                  "T3-ComPort...")
                If .IsOpen Then .DiscardInBuffer()
            End Try
        End With
    End Function
 
    Function Checksumme(ByVal Daten As Array) As Boolean
        Dim summe As Integer = 0
        For zähler As Integer = 2 To 39
            summe = summe + (Daten(zähler))
        Next
        summe = summe Mod 256
        If summe = 255 Then summe = 0
        If Daten(40) = summe Then
            Checksumme = True
        Else
            Checksumme = False
        End If
    End Function
 
    Private Sub Delay(ByVal Zeit As Integer)
        Dim Zeit1 As Integer = System.Environment.TickCount
        While (System.Environment.TickCount - Zeit1) < Zeit
            Application.DoEvents()
        End While
    End Sub
    Sub updateForm()
        TextBox1.Text = "Hallo"
    End Sub
End Class

    Private Sub verbinden_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles verbinden.Click
        With SerialPort1
            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()
                    verbinden.BackColor = Color.Green
                    verbinden.Text = "Verbunden"
                    Dim readThread As New Thread( 'Lesethread
                        Sub()
                            ReadSerialPort(SerialPort1)
                        End Sub)
                    readThread.Start()
                Catch ex As Exception
                    MessageBox.Show(ex.Message, "Fehler beim Open", _
                      MessageBoxButtons.OK, MessageBoxIcon.Error)
                    Exit Sub
                End Try
            End If
        End With
    End Sub
 
    'Wird im Lesethread aufgerufen
    Private Sub ReadSerialPort(port As SerialPort)
        ' Lesen
        While True
            ' 7 Bytes Head lesen
            Dim head As Byte() = New Byte(6) {}
            Dim headBytesRead As Integer = 0
 
            While headBytesRead < head.Length
                Dim read As Integer = port.Read(head, headBytesRead, head _
                  .Length - headBytesRead)
                headBytesRead += read
            End While
 
            'jetzt aus Head die Größe der restlichen Daten auslesen
            Dim restlicheGroesse As Integer = .....
            Dim body As Byte() = New Byte(restlicheGroesse - 1) {}
            Dim bodyBytesRead As Integer = 0
 
            While bodyBytesRead < restlicheGroesse
                Dim read As Integer = port.Read(body, bodyBytesRead , _
                  restlicheGroesse - bodyBytesRead )
                bodyBytesRead += read
            End While
 
            'GUI-Thread benachrichtigen, dass Telegramm empfangen wurde
            BeginInvoke(New Action(Of Byte(), Byte())(AddressOf _
              TelegramEmpfangen), head, body)
        End While
    End Sub
 
    'Wird im GUI-Thread aufgerufen, wenn Telegramm empfangen wurde
    Private Sub TelegramEmpfangen(head As Byte(), body As Byte())
        'Weiterverarbeiten..
    End Sub

 Private Sub verbinden_Click(ByVal sender As System.Object, ByVal e As _
   System.EventArgs) Handles verbinden.Click
        With SerialPort1
            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()
                    verbinden.BackColor = Color.Green
                    verbinden.Text = "Verbunden"
                Catch ex As Exception
                    MessageBox.Show(ex.Message, "Fehler beim Open", _
                      MessageBoxButtons.OK, MessageBoxIcon.Error)
                    Exit Sub
                End Try
            End If
        End With
    End Sub
 
 Private Sub Start_Click(sender As System.Object, e As System.EventArgs) _
   Handles Start.Click
        Dim start As New ParameterizedThreadStart(AddressOf ReadSerialPort)
        Dim empfangen As New Thread(start)
        empfangen.Start(SerialPort1)
    End Sub
 
   Private Sub ReadSerialPort(port As 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 = port.Read(head_array, headBytesRead, ( _
                  head_array.Length - headBytesRead))
                headBytesRead += read
            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 = port.Read(body_array, bodyBytesRead, _
                      parameterlänge - bodyBytesRead)
                    bodyBytesRead += read
                End While
                If Checksumme(head_array, body_array) = False Then
                    MsgBox("nicht ok")
                    port.DiscardInBuffer()
                Else
                    'GUI-Thread benachrichtigen, dass Telegramm empfangen wurde
                    BeginInvoke(New Action(Of Byte(), Byte())(AddressOf _
                      TelegramEmpfangen), head_array, body_array)
                End If
            Else
                port.DiscardInBuffer()
            End If
       Loop
    End Sub
 
 Function Checksumme(ByVal Hader_Daten As Array, ByVal Body_Daten As Array) As _
   Boolean
        Dim summe As Integer = 0
        For zähler As Integer = 2 To 6
            summe = summe + (Hader_Daten(zähler))
        Next
        For zähler As Integer = 0 To Body_Daten.Length - 2
            summe = summe + (Body_Daten(zähler))
        Next
        summe = summe Mod 256
        If summe = 255 Then summe = 0
        If Body_Daten(Body_Daten.Length - 1) = summe Then
            Checksumme = True
        Else
            Checksumme = False
        End If
    End Function
 
'Wird im GUI-Thread aufgerufen, wenn Telegramm empfangen wurde
Private Sub TelegramEmpfangen(head As Byte(), body As Byte())
        empfänger += 1
        TextBox1.Text = empfänger
End Sub

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

________
Alle Angaben ohne Gewähr. Keine Haftung für Vorschläge, Tipps oder sonstige Hilfe, falls es schiefgeht, nur Zeit verschwendet oder man sonst nicht zufrieden ist