CRC16问题求助！！
本人新手，正在做一个MODBUS协议的485通讯，其中关于CRC16校验一直得不到正确值。厂方给了一个例数：01 03 00 00 00 05 CRC:85 C9。我看到网上关于CRC的算法，就是将信息后面加16个0，然后再对0X18005进行异或计算，我用手算了一下得到了一个CRC值是F8 95。结果和我在单片机上用网上下载的一个函数得出的值相同。本以为是厂方给的例数错了，可是又下载了一个CRC16计算工具，算了一下，结果却是：85 C9。本人现在很迷惑，为什么会出现这种情况，不知道错在哪里，之后在网上又下载了几个程序，可是算出来的值更不一样。求高人指点我可能在哪里犯了什么错误。或者您如果有CRC16的程序，能计算出我给的例数的话，那麻烦您把程序给我一下。感激不尽啊！！ 算法
[解决办法]
http://blog.csdn.net/lluct/article/details/2617967
[解决办法]
楼主要确定自己的多项式是什么 CRC16分不少情况的
[解决办法]
你的应该是 CRC-16 Modbus 协议：
多项式：0x8005 (x^16 + x^15 + x^2 + 1)
初始值：0xFFFF
1 计算法：
Unsigned int crc_chk(unsigned char* data, unsigned char length)
{
int j;
unsigned int reg_crc=0xFFFF;
while(length--)
{
reg_crc ^= *data++;
for(j=0;j<8;j++)
{
if(reg_crc & 0x01) /* LSB(b0)=1 */
reg_crc=(reg_crc>>1) ^ 0xA001;
else
reg_crc=reg_crc >>1;
}
}
return reg_crc;
}
unsigned short int CRC16_IBM_16b_LookUpTable(unsigned char *nData, int No_of_bytes)
{
unsigned short int crc_16_table[16] = {
0x0000, 0xCC01, 0xD801, 0x1400, 0xF001, 0x3C00, 0x2800, 0xE401,
0xA001, 0x6C00, 0x7800, 0xB401, 0x5000, 0x9C01, 0x8801, 0x4400 };
unsigned short int CRC16IBM = 0xFFFF; //start
unsigned short int r;
/* while there is more data to process */
while (No_of_bytes-- > 0) {
/* compute checksum of lower four bits of *nData */
r = crc_16_table[CRC16IBM & 0xF];
CRC16IBM = (CRC16IBM >> 4) & 0x0FFF;
CRC16IBM = CRC16IBM ^ r ^ crc_16_table[*nData & 0xF];
/* now compute checksum of upper four bits of *nData */
r = crc_16_table[CRC16IBM & 0xF];
CRC16IBM = (CRC16IBM >> 4) & 0x0FFF;
CRC16IBM = CRC16IBM ^ r ^ crc_16_table[(*nData >> 4) & 0xF];
/* next... */
nData++;
}
return(CRC16IBM);
}
unsigned short int CRC16_IBM_256b_LookUpTable(unsigned char *nData, unsigned short int wLength)
{
unsigned short int wCRCTable[256] = {
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 };
unsigned char nTemp;
unsigned short int wCRCWord = 0xFFFF;//Start Value for the CRC16-IBM
while (wLength--)
{
nTemp = *nData++ ^ wCRCWord;
wCRCWord >>= 8;
wCRCWord ^= wCRCTable[nTemp];
}
return wCRCWord;
}
