Dim port As New IO.Ports.SerialPort("COM1")
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        Dim Buf(0) As Byte
        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