Modbus协议中CRC校验和LRC校验

1、CRC的生成循环冗余校验口域为两个字节，包含一个二进制16位值。附加在报文后面 的CRC的值由发送设备计算。接收设备在接收报文时重新计算CRC的值，并将计算 结果于实际接收到的CRC值相比较。如果两个值不相等，则为错误。CRC的计算，开始对一个16位寄存器预装全1.然后将报文中的连续的8位子节 对其进行后续的计算。只有字符中的8个数据位参与生成CRC的运算，起始位，停 止位和校验位不参与口计算。CRC的生成过程中，每个8 -位字符与寄存器中的值异或。然后结果向最低有 效位化58）方向移动6川代）1位，而最高有效位W58）位置充零。然后提取并检查 LSB：如果LSB为1,则寄存器中的值与一个固定

2、的预置值异或；如果LSB为0,则 不进行异或操作。这个过程将重复直到执行完8次移位。完成最后一次（第8次）移位及相关操 作后，下一个8位字节与寄存器的当前值异或，然后又同上面描述过的一样重复8次。 当所有报文中子节都运算之后得到的寄存器中的最终值，就是口.生成CRC的过程为：.将一个16位寄存器装入十六进制FFFF （全1）.将之称作口寄存器.将报文的第一个8位字节与16 （点CRC寄存器的低字节异或，结果置于CRC寄存 器.将CRC寄存器右移1位（向LSB方向），MSB充零.提取并检测LSB.（如果LSB为0）:重复步骤3 （另一次移位）.（如果LSB为1）:对CRC寄存器异或多项 式值 0

3、XA001 (1010 0000 0000 0001).可修编.重复步骤3和4,直到完成8次移位。当做完此操作后，将完成对8位字节的完 整操作。.对报文中的下一个字节重复步骤2到5,继续此操作直至所有报文被处理完毕。. CRC寄存器中的最终容为制值.当放置CRC值于报文时，如下面描述的那样，高低字节必须交换。MODBUS协议的口校验子程序代码为方便读者使用乂0口8兆协议，将VC、VB、ASM51环境下MODBUS协议的口校 验子程序代码一并给出，供读者参考。/*CRC Calculation for MODBUS Protocol for VC *数组5代为地址等传输字节，num为字节数，发为

4、6收为5unsigned int mb_crc(BYTE *snd,int num)(int i,j;unsigned int c,crc=0 xFFFFfor (i=0;inum;i )(c=sndi & 0 x00FF;crcFfor(j=0,j=1;crd=0 xA001;)elsecrc=1)return(crc);)unsigned short int CrcCheck(const unsigned char * buffer, const int buffLen)(unsigned short int crcValue = 0;if (!buffer | buffLen 0)(re

5、turn crcValue;)int CRCHi = 0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x1,0 xC0, 0 x80, 0 x41,0 x0,可修编0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x0, 0 xC1, 0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81, 0 x40, 0 x0, 0 xC1,0 x81,0

6、 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x1, 0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x1,0 xC0, 0 x80,

7、 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x0, 0 xC1,0 x81

8、,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x1,0 xC0, 0 x80, 0 x41, 0 x0, 0 xC1,0 x81,0 x40, 0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x1, 0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1, 0 x81,0 x40, 0 x0, 0 xC1,0

9、x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81, 0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x0, 0 xC1,0 x81,0 x40, 0 x1, 0 xC0, 0 x80, 0 x41,0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x0, 0 xC1,

10、 0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40, 0 x1,0 xC0, 0 x80, 0 x41,0 x1,0 xC0, 0 x80, 0 x41,0 x0, 0 xC1,0 x81,0 x40）；int CRCLo = 可修编0 x0, 0 xC0, 0 xC1,0 x1,0 xC3, 0 x3, 0 x2, 0 xC2, 0 xC6, 0 x6, 0 x7, 0 xC7, 0 x5, 0 xC5, 0 xC4, 0 x4, 0 xCC, 0 xC, 0 xD, 0 xCD, 0 xF, 0 xCF, 0 xCE

11、, 0 xE, 0 xA, 0 xCA, 0 xCB, 0 xB, 0 xC9, 0 x9, 0 x8, 0 xC8, 0 xD8, 0 x18, 0 x19, 0 xD9, 0 x1B, 0 xDB, 0 xDA, 0 x1A, 0 x1E, 0 xDE, 0 xDF, 0 x1F, 0 xDD, 0 x1D, 0 x1C, 0 xDC, 0 x14, 0 xD4, 0 xD5, 0 x15, 0 xD7, 0 x17, 0 x16, 0 xD6, 0 xD2, 0 x12, 0 x13, 0 xD3, 0 x11, 0 xD1,0 xD0, 0 x10, 0 xF0, 0 x30, 0 x

12、31,0 xF1,0 x33, 0 xF3, 0 xF2, 0 x32, 0 x36, 0 xF6, 0 xF7, 0 x37, 0 xF5, 0 x35, 0 x34, 0 xF4, 0 x3C, 0 xFC, 0 xFD, 0 x3D, 0 xFF, 0 x3F, 0 x3E, 0 xFE, 0 xFA, 0 x3A, 0 x3B, 0 xFB, 0 x39, 0 xF9, 0 xF8, 0 x38, 0 x28, 0 xE8, 0 xE9, 0 x29, 0 xEB, 0 x2B, 0 x2A, 0 xEA, 0 xEE, 0 x2E, 0 x2F, 0 xEF, 0 x2D, 0 xE

13、D, 0 xEC, 0 x2C, 0 xE4, 0 x24, 0 x25, 0 xE5, 0 x27, 0 xE7, 0 xE6, 0 x26, 0 x22, 0 xE2, 0 xE3, 0 x23, 0 xE1,0 x21,0 x20, 0 xE0, 0 xA0, 0 x60, 0 x61,0 xA1,0 x63, 0 xA3, 0 xA2, 0 x62, 0 x66, 0 xA6, 0 xA7, 0 x67, 0 xA5, 0 x65, 0 x64, 0 xA4, 0 x6C, 0 xAC, 0 xAD, 0 x6D, 0 xAF, 0 x6F, 0 x6E, 0 xAE, 0 xAA,

14、0 x6A, 0 x6B, 0 xAB, 0 x69, 0 xA9, 0 xA8, 0 x68, 0 x78, 0 xB8, 0 xB9, 0 x79, 0 xBB, 0 x7B, 0 x7A, 0 xBA, 0 xBE, 0 x7E, 0 x7F, 0 xBF, 0 x7D, 0 xBD, 0 xBC, 0 x7C, 0 xB4, 0 x74, 0 x75, 0 xB5, 0 x77, 0 xB7, 0 xB6, 0 x76, 0 x72, 0 xB2, 0 xB3, 0 x73, 0 xB1,0 x71,0 x70, 0 xB0, 0 x50, 0 x90, 0 x91,0 x51,0 x

15、93, 0 x53, 0 x52, 0 x92, 0 x96, 0 x56, 0 x57, 0 x97, 0 x55, 0 x95, 0 x94, 0 x54, 0 x9C, 0 x5C, 0 x5D, 0 x9D, 0 x5F, 0 x9F, 0 x9E, 0 x5E, 0 x5A, 0 x9A, 0 x9B, 0 x5B, 0 x99, 0 x59, 0 x58, 0 x98, 0 x88, 0 x48, 0 x49, 0 x89, 0 x4B, 0 x8B, 0 x8A, 0 x4A, 0 x4E, 0 x8E, 0 x8F, 0 x4F, 0 x8D, 0 x4D, 0 x4C, 0

16、x8C, 0 x44, 0 x84, 0 x85, 0 x45, 0 x87, 0 x47, 0 x46, 0 x86, 0 x82, 0 x42, 0 x43, 0 x83, 0 x41,0 x81,0 x80, 0 x40可修编);int i, m;int dCRCHi = 0 xFF;int dCRCLo = 0 xFF;for (i = 0; i buffLen; i+)(m = dCRCLo 八 bufferi;dCRCLo = dCRCHi 八 CRCHim;dCRCHi = CRCLom;)crcValue = dCRCLo + (dCRCHi 8);return crcValu

17、e;)|/*CRC Calculation for MODBUS Protocol for VB*Function mb_crc(ByRef snd() as BYTE,num as integer) as Longcrc_l=crc_h=&HFF可修编for i=1 to num crc_l=crc_l XOR snd(i) forj=1 to 8 if crc_l AND 1 then crc_l=(crc_l -1)/2 if crc_h and 1 then crc_l=crc_l 128 crc_h=(crc_h -1)/2 end ifcrc_l=crc_l XOR &HA0 cr

18、c_h=crc_h XOR &H01 else: crc_l=crc_l/2 if crc_h and 1 then crcl_l=crc_l 128 crc_h=(crc_h -1)/2 else: crc_h=crc_h/2 end if end if next j next imb_crc=crc_l crc_h*256 End Function可修编;CRC Calculation for MODBUS Protocol for ASM51；R1为发送（接收）字节的缓存首地址;R2为发送（接收）字节的字节数（不含制字节），;R3为制校验低位字节，;R4为制校验高位字节，CRC: MOV

19、 A,#0FFHMOV R4,AMOV R3,ACRC1: MOV A,R1XRL A,R3MOV R3,AMOV R2,#08HCRC8: CLR CMOV A,R4RRC AMOV R4,AMOV A,R3RRC AMOV R3,AJNC CRC10MOV A,R3可修编XRL A,#01HMOV R3,AMOV A,R4XRL A,#0A0HMOV R4,ACRC10: DJNZ R2,CRC8INC R1DJNZ CRC1RETLRC的生成纵向冗余校验（LRC）为一个字节，含有8位二进制值。LRC由发送设备计算，并附加LRC到报文。接收设备在接收文时计算LRC,并将计算的结果与在1口接收到的实 际值相比较，如果两个值不相等，则结果为错。LRC的计算，对报文中的所有的连续8位字节相加，忽略任何进位，然后求出其二 进制补码。LRC为一个8位域，那么每个会导致值大于255新的相加只是简单的将域的值在零” 回绕”。因为没有第9位，进位被自动放弃。生成一个LRC的过程为：.不包括起始“冒号”和结束CRLF的