CRC校驗(yàn)碼簡(jiǎn)介及CRC16的計(jì)算方法
[導(dǎo)讀]什么是CRC校驗(yàn)？CRC即循環(huán)冗余校驗(yàn)碼（Cyclic Redundancy Check）：是數(shù)據(jù)通信領(lǐng)域中最常用的一種查錯(cuò)校驗(yàn)碼，其特征是信息字段和校驗(yàn)字段的長(zhǎng)度可以任意選定。奇偶校驗(yàn)雖然簡(jiǎn)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(lái)校驗(yàn)。CRC也稱為多項(xiàng)式碼。
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什么是CRC校驗(yàn)？
CRC即循環(huán)冗余校驗(yàn)碼（Cyclic Redundancy Check）：是數(shù)據(jù)通信領(lǐng)域中最常用的一種查錯(cuò)校驗(yàn)碼，其特征是信息字段和校驗(yàn)字段的長(zhǎng)度可以任意選定。奇偶校驗(yàn)雖然簡(jiǎn)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(lái)校驗(yàn)。CRC也稱為多項(xiàng)式碼。
循環(huán)冗余檢查（CRC）是一種數(shù)據(jù)傳輸檢錯(cuò)功能，對(duì)數(shù)據(jù)進(jìn)行多項(xiàng)式計(jì)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(jìn)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(yàn)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：
| 地址 | 功能碼 | 數(shù)據(jù)信息 | 校驗(yàn)碼 |
|---|---|---|---|
| 1byte | 1byte | N byte | 2byte |
其中2 Byte的校驗(yàn)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(yàn)碼計(jì)算方法
1. 計(jì)算法
此方法缺點(diǎn)是計(jì)算量大，有時(shí)不方便使用在單片機(jī)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(yǔ)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(yàn)位低8位
???????checkBitHig?=?(unsigned?char)((crc?>>?8)?&?0xff);?//校驗(yàn)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(cè)試結(jié)果：
在線CRC校驗(yàn)網(wǎng)址
將 01 03 00 00 00 02 代入下面網(wǎng)址驗(yàn)證：
-
CRC在線校驗(yàn)地址 https://www.lammertbies.nl/comm/info/crc-calculation.html
-
專門的在線校驗(yàn)計(jì)算器：16進(jìn)制(CRC16)(MODBUS RTU通訊)校驗(yàn)碼在線計(jì)算器 https://www.23bei.com/tool-59.html
-
CRC校驗(yàn)工具 http://www.metools.info/code/c15.html
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