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我设计了一个应用程序，它通过 USB-> 串行适配器（Windows 7 64bit，VS2013，针对.Net Framework 3.5 SP1）与我的开发盒上的外部设备进行通信。我还有一个带有 Windows XP SP3 和 .Net Framework 3.5 SP1 的本机串行端口的测试盒设置。外接设备在 19200,N,8,1 通信，支持硬件流控。我知道流量控制有效，因为当我在设备上启动报告时，将流量控制设置为无并手动创建一个复选框来打开和关闭 DTR，当 DTR 关闭时，设备将暂停。

但是，我无法通过我的 Windows 桌面应用程序使硬件流控制自动工作（Handshake.RequestToSend）。如果我将握手设置为无，则通信“通常”是成功的。有时在具有本机串行端口的较慢测试盒上，我相信当从设备请求大量数据时接收缓冲区会溢出，即使我设置了一个非常大的缓冲区并使 DataReceived 例程尽可能高效。我在驱动程序本身中尝试了各种流量控制设置，但没有任何效果。如果我在我的应用程序中将握手设置为 RequestToSend，通信似乎会停止，并且设备永远不会响应我的初始状态请求。我尝试了 True/False 与 DtrEnable 和 RtsEnable 的各种组合，但无济于事。我' 我在互联网上搜索了好几个小时，但到目前为止还没有看到任何有用的东西。这是我的一些代码：

  Private sbReceive_Extract As New StringBuilder 'Receive buffer

  Private WithEvents comPort As SerialPort

  Private bReady as Boolean = False 'data ready flag

  Private bExtract as Boolean = False 'type of data request

  Public Sub Status_Request()

    sbReceive_Extract.Length = 0 'clear buffer

    If Open_Port() = True

      comPort.DiscardInBuffer()
      comPort.DiscardOutBuffer()

      'Send status request to external serial device
      comPort.Write(Chr(27) & "?" & Chr(13))

      bExtract = False 'Just get status header this time    

      'Loop until device responds to request
      bReady = False
      Do Until bReady = True
        Application.DoEvents()
        'update an onscreen status label as buffer fills
        lblStatus.Text = "Buffer read: " & sbReceive_Extract.Length.ToString
      Loop

    End If

  End Sub


  Public Function Open_Port() As Boolean

      'return code for port open or closed
    Dim bReturnResult As Boolean = False

    If comPort Is Nothing Then
      comPort = New SerialPort
    End If

    Try
      With comPort
        .PortName = "COM1"       'comm port 1
        .BaudRate = 19200  'transfer speed
        .DataBits = 8       '8 bits
        .StopBits = StopBits.One
        .Parity = Parity.None
        .ReadBufferSize = 32768 '32768=size of buffer in bytes
        .ReadTimeout = SerialPort.InfiniteTimeout
        .Handshake = Handshake.RequestToSend 'works when set to none
        .DtrEnable = True 'tried both true/false
        .RtsEnable = True 'tried both true/false
        .Encoding = Encoding.Default
        .NewLine = Chr(13) '13=carriage return
        .ReceivedBytesThreshold = 1
      End With

      If comPort.IsOpen = False Then
        comPort.Open()
      End If

      If comPort.IsOpen = True Then
        bReturnResult = True
      Else
        bReturnResult = False
      End If

    Catch Ex As Exception
      bReturnResult = False
    End Try

    Return bReturnResult

  End Function

Private Sub comVoteExt_DataReceived(ByVal sender As SerialPort, ByVal eArgs As SerialDataReceivedEventArgs) 处理 comVoteExt.DataReceived

Dim sData As Integer = 0 'integer to hold serial data

Try
  Do
    sData = sender.ReadChar 'take one char off the stack
    sbReceive_Extract.Append(Chr(sData))
    If bExtract = True Then
      'Check for data
      If iLength = 0 Then
          'hex 04 is end of data on tally stream
        If Chr(sData) = Chr("&H04") Then
          iLength = sbReceive_Extract.Length
        End If
      Else
           '6 bytes reserved for checksum and carriage return
        If sbReceive_Extract.Length >= iLength + 6 Then
            'Meets checksum length. Ready for next stage.
          bReady = True
        End If
      End If
    Else
        '20 bytes of header information 
      If sbReceive_Extract.Length > 20 Then
          'Data is ready for next stage. Minimum header length met.
        bReady = True
      End If
    End If
  Loop Until sender.BytesToRead = 0
Catch exc As Exception
End Try

结束子

有什么看起来可能导致我的握手问题吗？一旦端口打开以开始通信，是否有某种方法可以“唤醒”设备？我尝试在端口打开后将 DTREnable 设置为 true，但这似乎并不重要。我很困惑。

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