Private Delegate Sub DelegatTextInTextbox(Text As String)
 
Private Sub SerialPort1_PinChanged(ByVal sender As System.Object, ByVale As _
  System.IO.Ports.SerialPinChangedEventArgs) Handles SerialPort1.PinChanged
      TextInTextbox("DSR auf 1")
End Sub
 
Private Sub TextInTextbox(DeinText As String)
    If Me.TextBox1.InvokeRequired Then
         Dim d As New DelegatTextInTextbox(AddressOf TextInTextbox)
         Me.Invoke(d, New Object() {DeinText})
    Else
          Me.TextBox1.Text = DeinText
    End If
End Sub