/**
     * CRC检验值
     * @param modbusdata
     * @param length
     * @return CRC检验值
     */
    protected int crc16_modbus(byte[] modbusdata, int length)
    {
        int i=0, j=0;
        int crc = 0xffff;//有的用0,有的用0xff
        try
        {
            for (i = 0; i < length; i++)
            {
                //注意这里要&0xff,因为byte是-128~127,&0xff 就是0x0000 0000 0000 0000  0000 0000 1111 1111
                //参见:https://blog.csdn.net/ido1ok/article/details/85235955
                crc ^= (modbusdata[i]&(0xff));
                for (j = 0; j < 8; j++)
                {
                    if ((crc & 0x01) == 1)
                    {
                        crc = (crc >> 1) ;
                        crc = crc ^ 0xa001;
                    }
                    else
                    {
                        crc >>= 1;
                    }
                }
            }
        }
        catch (Exception e)
        {

        }

        return crc;
    }

    /**
     * CRC校验正确标志
     * @param modbusdata
     * @param length
     * @return 0-failed 1-success
     */
    protected int crc16_flage(byte[] modbusdata, int length)
    {
        int Receive_CRC = 0, calculation = 0;//接收到的CRC,计算的CRC

        Receive_CRC = crc16_modbus(modbusdata, length);
        calculation = modbusdata[length + 1];
        calculation <<= 8;
        calculation += modbusdata[length];
        if (calculation != Receive_CRC)
        {
            return 0;
        }
        return 1;
    }