/// <summary>
        /// CRC计算
        /// </summary>
        /// <param name="arr">源数据</param>
        /// <param name="seat">开始位置</param>
        /// <param name="len">长度</param>
        /// <returns></returns>
        public static byte [] Crc(byte[] arr, UInt16 seat, UInt32 len)
        {

            UInt32 i;
            UInt16 j, uwCrcReg = 0xFFFF;

            for (i = seat; i < (len); i++)
            {
                uwCrcReg ^= arr[i];
                for (j = 0; j < 8; j++)
                {
                    if ((uwCrcReg & 0x0001) != 0)
                    {
                        uwCrcReg = (UInt16)((UInt16)(uwCrcReg >> 1) ^ (UInt16)0xA001);
                    }
                    else
                    {
                        uwCrcReg = (UInt16)(uwCrcReg >> 1);
                    }
                }
            }
            byte [] CRC=new byte[2];
            CRC[0] = (byte)(uwCrcReg);
            CRC[1] = (byte)(uwCrcReg >> 8);
            return CRC;
        }