[.NET] VS.2005下RS232的問題~請問程式碼哪裡出錯了？

[fire2 ( q )]

在這邊ㄧ直接收不到資料
其中出錯的地方都是在

Dim Incoming As String = com1.ReadLine()
後面的com1.ReadLine()這部份

試了好久，還是找不到錯誤
所以來這邊請較ㄧ下

我是用COM1做測試



    '將字串傳送至序列埠
    Sub SendSerialData(ByVal data As String)
        ' Send strings to a serial port.
        Using com1 As IO.Ports.SerialPort = My.Computer.Ports.OpenSerialPort("C
OM1")
            com1.WriteLine(data)
        End Using
    End Sub

    '接收來自序列埠的字串
    Function ReceiveSerialData() As String
        ' Receive strings from a serial port.
        Dim returnStr As String = ""

        Using com1 As IO.Ports.SerialPort = My.Computer.Ports.OpenSerialPort("C
OM1")
            Do
                Dim Incoming As String = com1.ReadLine()
                If Incoming Is Nothing Then
                    Exit Do
                Else
                    returnStr &= Incoming & vbCrLf
                End If
            Loop
        End Using

        Return returnStr
    End Function

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→ fire2:我是參考這邊的資料http://0rz.net/491pC