CRC校驗碼簡介及CRC16的計算方法

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什么是CRC校驗？

CRC即循環(huán)冗余校驗碼（Cyclic Redundancy Check）：是數(shù)據(jù)通信領(lǐng)域中最常用的一種查錯校驗碼，其特征是信息字段和校驗字段的長度可以任意選定。奇偶校驗雖然簡單，但是漏檢率太高，而CRC則要低的多，所以大多數(shù)都是使用CRC來校驗。CRC也稱為多項式碼。

循環(huán)冗余檢查（CRC）是一種數(shù)據(jù)傳輸檢錯功能，對數(shù)據(jù)進行多項式計算，并將得到的結(jié)果附在幀的后面，接收設(shè)備也執(zhí)行類似的算法，進而可以保證在軟件層次上數(shù)據(jù)傳輸?shù)恼_性和完整性。

CRC-16校驗碼的應(yīng)用

根據(jù)Modbus協(xié)議，常規(guī)485通訊的信息發(fā)送形式如下：

其中2 Byte的校驗碼一般就是采用CRC16。

我們之前的網(wǎng)文《485型風(fēng)速和風(fēng)向變送器數(shù)據(jù)包解析》中介紹的通訊協(xié)議就是16位CRC碼。

CRC-16校驗碼計算方法

1. 計算法

此方法缺點是計算量大，有時不方便使用在單片機中。

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????????{
??????????????crc?=?calccrc(*buf,?crc);

??????????????buf++;
???????}

???????hi?=?crc?%?256;

???????lo?=?crc?/?256;

???????crc?=?(hi?<8)?|?lo;

???????return?crc;

}

2. 查表法

速度快，語句少，但表格占用一定的程序空間。

//?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????????{
??????????????iIndex?=?CRCHi?^?pBuffer[i];

??????????????CRCHi?=?CRCLo?^?aucCRCHi[iIndex];

??????????????CRCLo?=?aucCRCLo[iIndex];
???????}

???????return?(unsigned?int)(?CRCHi?<}

函數(shù)調(diào)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);?//校驗位低8位

???????checkBitHig?=?(unsigned?char)((crc?>>?8)?&?0xff);?//校驗位高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);
}

測試結(jié)果：

在線CRC校驗網(wǎng)址

將 01 03 00 00 00 02 代入下面網(wǎng)址驗證：

1. CRC在線校驗地址
   https://www.lammertbies.nl/comm/info/crc-calculation.html

2. 專門的在線校驗計算器：16進制(CRC16)(MODBUS RTU通訊)校驗碼在線計算器
   https://www.23bei.com/tool-59.html
   

3. CRC校驗工具
   http://www.metools.info/code/c15.html