串口发送请求，和接受数据 一

 /// <summary>
        /// Reading and writing.
        /// </summary>
        [DllImport("kernel32.dll", SetLastError = true)]
        internal static extern Boolean WriteFile(IntPtr fFile, Byte[] lpBuffer, UInt32 nNumberOfBytesToWrite,
            out UInt32 lpNumberOfBytesWritten, IntPtr lpOverlapped);

这个是来发送bytes到COM口。

 /// <summary>
        /// Queues bytes for transmission. 
        /// </summary>
        /// <param name="tosend">Array of bytes to be sent</param>
        public void Send(byte[] tosend)
        {
            uint sent = 0;
            CheckOnline();
            CheckResult();
            writeCount = tosend.GetLength(0);
            if (Win32Com.WriteFile(hPort, tosend, (uint)writeCount, out sent, ptrUWO))
            {
                writeCount -= (int)sent;
            }
            else
            {
                int error = Marshal.GetLastWin32Error() ;
                if (error != Win32Com.ERROR_IO_PENDING)
                {
                    ThrowException("Unexpected failure");
                }
                //else
                //{
                //    DateTime maxTime = DateTime.Now.AddSeconds(2);
                //    while (maxTime > DateTime.Now && sent!=6)
                //    {                       
                //        Win32Com.GetOverlappedResult(hPort, ptrUWO, out sent, false);
                //    }                   
                //}
            }
        }