Public Class Form1
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        End
    End Sub
    Dim parity As IO.Ports.Parity
    Dim stopbits As IO.Ports.StopBits
    Dim port As IO.Ports.SerialPort = New IO.Ports.SerialPort("COM1", 9600, _
      parity.Even, 7, stopbits.One)
    Dim cardnr As String
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        Dim Buf(0) As Byte
        port.Open()
        If port.BaseStream.CanRead Then
            port.BaseStream.BeginRead(Buf, 0, 1, AddressOf ondatareceived, Buf)
        End If
    End Sub
 
    Sub ondatareceived(ByVal ar As IAsyncResult)
        Dim buf() As Byte = CType(ar.AsyncState, Byte())
        ListBox1.Items.Add(buf(0).ToString)
        If port.BaseStream.CanRead Then
            port.BaseStream.BeginRead(Buf, 0, 1, AddressOf ondatareceived, Buf)
        End If
 
    End Sub
 
End Class