RS232 with API

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C#

I'm sorry and my english is poor. If you can't understand what i mean and tell me, please! Because of I need your help.
When I communication to board through RS232 with API, but my program will be stopped in ReadFile() after running for a long time. There is a progarm below and happen to boldface. I can't find a answer and can't solve it. I have setted up timeout but it seems like don't active. Even through time is over but my program don't go next step. Something wrong with my program. Please give me a advice. Thanks.
(some classes I simplied it because it's all API's function)

const Int32 INVALID_HANDLE_VALUE = -1;
System.IntPtr handle = (IntPtr)INVALID_HANDLE_VALUE;
DCB dcb = new DCB();  //class of DCB
CommTimeouts timeouts = new CommTimeouts(); //

private void Run()
{
   readthread = true;
   byte[] bufferr = new byte[230];
   int reclength = SendByte[5] * 2 + 5;
   System.Text.ASCIIEncoding Encoding = new System.Text.ASCIIEncoding();
   int written = 0;
   int readed = 0;
   int secondnow;
   int secondold;
   byte[] SendByte = new byte[8];

   do
   {
      if (handle == (IntPtr)INVALID_HANDLE_VALUE)
      {
        handle = CreateFile("COM7", GENERIC_READ | GENERIC_WRITE, 0, 0, 
                 OPEN_EXISTING, 0, 0);
        Thread.Sleep(1);
        GetCommState(handle, dcb);
        dcb.BaudRate = 57600;
        dcb.Parity = 0;         //無
        dcb.ByteSize = 8;       //資料位元
        dcb.StopBits = 1;
        SetCommState(handle, dcb);
        
        timeouts.ReadIntervalTimeout = 0;
        timeouts.ReadTotalTimeoutMultiplier = 0;
        timeouts.ReadTotalTimeoutConstant = 500;       
        timeouts.WriteTotalTimeoutMultiplier = 0;                      
        timeouts.WriteTotalTimeoutConstant = 500;                    
        IntPtr a = API_RS232.SetCommTimeouts(handle,ref timeouts);
        Thread.Sleep(1);
      }

      if (handle != (IntPtr)INVALID_HANDLE_VALUE)
      {
        WriteFile(handle,SendByte,(uint)SendByte.Length,ref written, 0);
        Thread.Sleep(50);
      }

      if (handle != (IntPtr)INVALID_HANDLE_VALUE)
      {
        ReadFile(handle, bufferr,(uint)reclength,ref readed,  
                     0);                   
      }

      Thread.Sleep(50);
    }