Why can't this code open a serial port?

Public Class my_class

Dim WithEvents COMPort As New System.IO.Ports.SerialPort

Public Sub FindReader()

    Dim ports As String() = IO.Ports.SerialPort.GetPortNames()
    Dim port As String
    For Each port In ports
        MsgBox(port, MsgBoxStyle.OkOnly Or MsgBoxStyle.Exclamation, "Serial port detecetd")
    Next port


  If COMPort.IsOpen Then
     COMPort.RtsEnable = False
     COMPort.DtrEnable = False
     COMPort.Close()
     System.Threading.Thread.Sleep(200)
  End If

    COMPort.PortName = "COM1"
    COMPort.BaudRate = 9600
    COMPort.DataBits = 8
    COMPort.Parity = IO.Ports.开发者_JAVA百科Parity.None
    COMPort.StopBits = IO.Ports.StopBits.One
    COMPort.Handshake = IO.Ports.Handshake.RequestToSend
    COMPort.ReadTimeout = 2000 
    COMPort.WriteTimeout = -1
    COMPort.NewLine = Chr(13)
    COMPort.ReadBufferSize = 12
    COMPort.ReceivedBytesThreshold = COMPort.ReadBufferSize

  Try
     COMPort.Open()
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try

  If COMPort.IsOpen Then
     COMPort.RtsEnable = True
     COMPort.DtrEnable = True

     'Kick start the serial port so it starts reading data.
     COMPort.BreakState = True
     System.Threading.Thread.Sleep(CInt(11000 / COMPort.BaudRate) + 2)   ' Min. 11 bit delay (startbit, 8 data bits, parity bit, stopbit
     COMPort.BreakState = False

     MsgBox(COMPort.PortName & " opened at " & COMPort.BaudRate.ToString & " baud", MsgBoxStyle.OkOnly Or MsgBoxStyle.Exclamation, "FindReader()")

  End If
 End Sub

When it runs, it shows a single COM port "COM1". I am assured that the device attached to it is a standard 8,n,1 and uses 9,600 baud.

The exception is "Acess to the port 'COM1' is denied". Any ideas?

Access denied might mean that the has already been opened by another application.

Are you able to open the port using another, known-good application, for example Hyperterminal?

[Because if you're not, then the problem isn't with your code.]

Alternatively, I think that Portmon can be used to determine which other process (if any) has already opened the port.