一、CRC16簡介
      迴圈冗餘碼CRC檢驗技術廣泛應用於測控及通訊領域。CRC計算可以靠專用的硬體來實現，但是對於低成本的微控制器系統，在沒有硬體支援下實現CRC檢驗，關鍵的問題就是如何通過軟體來完成CRC計算，也就是CRC演算法的問題。下面給出按位元組計算CRC16的演算法。
二、CRC16演算法
其原理是：CRC碼一般在k位資訊位之後拼接r位校驗位生成。編碼步驟如下：
（1）將待編碼的k位資訊表示成多項式 M(x)。
（2）將 M(x)左移 r 位，得到 M(x)*xr 。
（3）用r+1位的生成多項式G(x)去除M(x)*xr 得到餘數R(x)。
（4）將M(x)*xr 與R(x)作模2加，得到CRC碼。

例子：已知資訊位為1100，生成多項式G(x) = x3+x+1，求CRC碼。
M(x) = 1100 M(x)*x3 = 1100000 G(x) = 1011
M(x)*x3 / G(x) = 1110 + 010 /1011 R(x) = 010
CRC碼為： M(x)*x 3+R(x)=1100000+010 =1100010

三、CRC16演算法軟體實現

程式碼如下：

quint16 KSEView::McMBCRC16(QByteArray &pDataIn, int iLenIn){
    quint8 buf;
    quint16 crc16 = 0xFFFF;
    static const quint16 crc16Table[] =
    { 
      0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
      0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
      0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
      0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
      0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
      0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
      0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
      0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
      0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
      0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
      0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
      0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
      0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
      0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
      0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
      0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
      0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
      0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
      0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
      0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
      0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
      0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
      0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
      0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
      0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
      0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
      0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
      0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
      0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
      0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
      0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
      0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
    };
    
    for ( auto i = 0; i < iLenIn; ++i )
    {
        buf = pDataIn.at( i ) ^ crc16;
        crc16 >>= 8;
        crc16 ^= crc16Table[ buf ];
    }
    return (crc16);
}

void KSEView::Request04(unsigned char id, unsigned int address, unsigned int dLong){
    QByteArray SenData;
    SenData.resize(8);
    SenData[0]=id;
    SenData[1]=04;
    SenData[2]=address>>8;
    SenData[3]=address&0xFF;
    SenData[4]=dLong>>8;
    SenData[5]=dLong&0xFF;
    quint16 CrcTemp = McMBCRC16(SenData,6);
    SenData[6]=CrcTemp&0xFF;
    SenData[7]=CrcTemp>>8;
    qDebug()<<"crc"<<SenData;
    //myserial->write((const char *)SenData,8);
    sendDataKSE(SenData);
}