CRC校验码简介及CRC16的计算方法

什么是CRC校验?

CRC即循环冗余校验码(Cyclic Redundancy Check):是数据通信领域中最常用的一种查错校验码,其特征是信息字段和校验字段的长度可以任意选定。奇偶校验虽然简单,但是漏检率太高,而CRC则要低的多,所以大多数都是使用CRC来校验。CRC也称为多项式码。

循环冗余检查(CRC)是一种数据传输检错功能,对数据进行多项式计算,并将得到的结果附在帧的后面,接收设备也执行类似的算法,进而可以保证在软件层次上数据传输的正确性和完整性。

CRC-16校验码的应用

根据Modbus协议,常规485通讯的信息发送形式如下:

其中2 Byte的校验码一般就是采用CRC16。

我们之前的网文《485型风速和风向变送器数据包解析》中介绍的通讯协议就是16位CRC码。

CRC-16校验码计算方法

1. 计算法

此方法缺点是计算量大,有时不方便使用在单片机中。

unsigned int calccrc(unsigned char crcbuf, unsigned int crc)
{
       unsigned char i;

       crc = crc ^ crcbuf;

       for (i = 0; i < 8; i++)
       {
              unsigned char chk;

              chk = crc & 1;

              crc = crc >> 1;

              crc = crc & 0x7fff;

              if (chk == 1)

                     crc = crc ^ 0xa001;

              crc = crc & 0xffff;
       }

       return crc;
}

unsigned int chkcrc(unsigned char *buf, unsigned char len)
{
       unsigned char hi, lo;

       unsigned int i;

       unsigned int crc;

       crc = 0xFFFF;

       for (i = 0; i < len; i++)
       {
              crc = calccrc(*buf, crc);

              buf++;
       }

       hi = crc % 256;

       lo = crc / 256;

       crc = (hi << 8) | lo;

       return crc;

}

2. 查表法

速度快,语句少,但表格占用一定的程序空间。

// 逆序CRC表

unsigned char aucCRCHi[]{

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

       0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

       0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

       0x00, 0xC1, 0x81, 0x40

};

unsigned char aucCRCLo[]{

       0x00, 0xC0, 0xC1, 0x01, 0xC3, 0x03, 0x02, 0xC2, 0xC6, 0x06, 0x07, 0xC7,

       0x05, 0xC5, 0xC4, 0x04, 0xCC, 0x0C, 0x0D, 0xCD, 0x0F, 0xCF, 0xCE, 0x0E,

       0x0A, 0xCA, 0xCB, 0x0B, 0xC9, 0x09, 0x08, 0xC8, 0xD8, 0x18, 0x19, 0xD9,

       0x1B, 0xDB, 0xDA, 0x1A, 0x1E, 0xDE, 0xDF, 0x1F, 0xDD, 0x1D, 0x1C, 0xDC,

       0x14, 0xD4, 0xD5, 0x15, 0xD7, 0x17, 0x16, 0xD6, 0xD2, 0x12, 0x13, 0xD3,

       0x11, 0xD1, 0xD0, 0x10, 0xF0, 0x30, 0x31, 0xF1, 0x33, 0xF3, 0xF2, 0x32,

       0x36, 0xF6, 0xF7, 0x37, 0xF5, 0x35, 0x34, 0xF4, 0x3C, 0xFC, 0xFD, 0x3D,

       0xFF, 0x3F, 0x3E, 0xFE, 0xFA, 0x3A, 0x3B, 0xFB, 0x39, 0xF9, 0xF8, 0x38,

       0x28, 0xE8, 0xE9, 0x29, 0xEB, 0x2B, 0x2A, 0xEA, 0xEE, 0x2E, 0x2F, 0xEF,

       0x2D, 0xED, 0xEC, 0x2C, 0xE4, 0x24, 0x25, 0xE5, 0x27, 0xE7, 0xE6, 0x26,

       0x22, 0xE2, 0xE3, 0x23, 0xE1, 0x21, 0x20, 0xE0, 0xA0, 0x60, 0x61, 0xA1,

       0x63, 0xA3, 0xA2, 0x62, 0x66, 0xA6, 0xA7, 0x67, 0xA5, 0x65, 0x64, 0xA4,

       0x6C, 0xAC, 0xAD, 0x6D, 0xAF, 0x6F, 0x6E, 0xAE, 0xAA, 0x6A, 0x6B, 0xAB,

       0x69, 0xA9, 0xA8, 0x68, 0x78, 0xB8, 0xB9, 0x79, 0xBB, 0x7B, 0x7A, 0xBA,

       0xBE, 0x7E, 0x7F, 0xBF, 0x7D, 0xBD, 0xBC, 0x7C, 0xB4, 0x74, 0x75, 0xB5,

       0x77, 0xB7, 0xB6, 0x76, 0x72, 0xB2, 0xB3, 0x73, 0xB1, 0x71, 0x70, 0xB0,

       0x50, 0x90, 0x91, 0x51, 0x93, 0x53, 0x52, 0x92, 0x96, 0x56, 0x57, 0x97,

       0x55, 0x95, 0x94, 0x54, 0x9C, 0x5C, 0x5D, 0x9D, 0x5F, 0x9F, 0x9E, 0x5E,

       0x5A, 0x9A, 0x9B, 0x5B, 0x99, 0x59, 0x58, 0x98, 0x88, 0x48, 0x49, 0x89,

       0x4B, 0x8B, 0x8A, 0x4A, 0x4E, 0x8E, 0x8F, 0x4F, 0x8D, 0x4D, 0x4C, 0x8C,

       0x44, 0x84, 0x85, 0x45, 0x87, 0x47, 0x46, 0x86, 0x82, 0x42, 0x43, 0x83,

       0x41, 0x81, 0x80, 0x40
};

unsigned short GetQuickCRC16(unsigned char * pBuffer, int Length) 
{

       unsigned char CRCHi = 0xFF;

       unsigned char CRCLo = 0xFF;

       unsigned char iIndex = 0;

       for (int i = 0; i < Length; i++)
       {
              iIndex = CRCHi ^ pBuffer[i];

              CRCHi = CRCLo ^ aucCRCHi[iIndex];

              CRCLo = aucCRCLo[iIndex];
       }

       return (unsigned int)( CRCHi << 8 | CRCLo);// CRC校验返回值 
}

函数调用

int main()
{
       unsigned char checkBitLow, checkBitHig;

       unsigned char pCharData[6] = { 0x01 ,0x03,0x00,0x00,0x00,0x02 };

       unsigned int crc = chkcrc(pCharData, 6);

       checkBitLow = (unsigned char)(crc & 0xff); //校验位低8位

       checkBitHig = (unsigned char)((crc >> 8) & 0xff); //校验位高8位

       printf ("chkcrc checkBitLow:%02X checkBitHig:%02X \n", checkBitHig, 
checkBitLow);

       crc = GetQuickCRC16(pCharData, 6);

       checkBitLow = (unsigned char)(crc & 0xff);

       checkBitHig = (unsigned char)((crc >> 8) & 0xff);

       printf("GetQuickCRC16 checkBitLow:%02X checkBitHig:%02X \n", checkBitHig, checkBitLow);
}

测试结果:

在线CRC校验网址

 01 03 00 00 00 02 代入下面网址验证:

  1. CRC在线校验地址https://www.lammertbies.nl/comm/info/crc-calculation.html

  1. 专门的在线校验计算器:16进制(CRC16)(MODBUS RTU通讯)校验码在线计算器https://www.23bei.com/tool-59.html

  1. CRC校验工具http://www.metools.info/code/c15.html

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