A.1 CRC16 算法

A.1.1 CRC16 算法参数设置

CRC16 算法中要求了 Counter、Data ID、CRC 等参数设置。

A.1.2 Length

在 CRC16 算法中，在每次发送的数据长度可能变化时，可使用 Length 表示本次发送的
数据的长度，Length = CRC + Counter +Length。

A.1.3 Counter

在 CRC16 算法中，发送方在第一次发送时将 Counter 置为 0，并在后续每次发送时将Counter 加 1。当 Counter 值达到 255(0xFF)后，发送方的下一次发送将 Counter 重新置为 0。
接收节点在接收到报文后对 Counter 值进行监控：
a）连续接收到 4 个周期 Counter 值相同时不计为错误，但在随后第 5 个周期中 Counter值仍相同时，需记录 Counter 错误；
b）当连续接收到连续 3 个周期的 Counter 差值≥2 时，需记录 Counter 错误；当检查到 Counter 错误时，将使用信号定义的 Invalid 值或替代值，直到 Counter 值恢复连续为止。

A.1.4 Data ID

在 CRC16 算法中，Data ID 的 2 个字节(16bits)都会包含在 CRC 计算中。在计算时，将Data ID 加入在需保护数据之后。

A.1.5 CRC

在 CRC16 算法中，CRC 算法规则为：0x1021(x16+x12+x5+1)，初始值为 0xFF，XOR 值为0x00
在 CRC 计算时，计算示例见图
a）首先计算在总线上发送的需要保护的信号/信号组(不包含 CRC 字段)
b）其次计算 Data ID 的两个字节，先高字节后低字节；

A.1.6 CRC16 算法示例

a）数据标识符(Data ID)：0x1234
b）需保护的数据(Protected Data)：0x11 0x22 0x33 0x44 0x55 0x66 0x77 0x88
c）Counter = 0x01；Length = 0x000D；
d）CRC16_Checksum = CRC16(0x11 0x22 0x33 0x44 0x55 0x66 0x77 0x88 0x01 0x00 
0x0D 0x12 0x34)
e）CRC16_checksum = 0x821A

A.1.7 CRC16 算法推荐(查表法)

/*定义 CRC16(计算规则 0x1021)的查表的表格*/
const uint16_t crc_table[256] ={
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0};
7
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* * CRC 校验子程序 0x1021(x16+x12+x5+1) * * * * * * * * * * * *
* * 参数 1，uint8_t *data：需要计算的数据 * * * * * * * * * * *
* * 参数 1，uint16_t len：需要计算的数据字节长度 * * * * * * * *
* * 返回值，uint16_t crc16：计算出的 CRC 值 * * * * * * * * * * *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
uint16_t crc_16(uint8_t *data, uint16_t len)
{
 uint16_t crc16 = 0xFFFF; //定义 CRC 计算的初始值
 uint16_t crc_high8, crc_low8;
 while( len-- ) {
 crc_high8 = (crc16 >> 8);
 crc_low8 = (crc16 << 8);
 crc16 = crc_low8 ^ crc_table[crc_high8 ^ *data];
 data++;
 }
 return crc16;
}

A.1.8 CRC16 实例(查表法)

查表法
#include<stdio.h>
const unsigned short crc_table[256] ={
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0};
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* * CRC 校验子程序 0x1021(x16+x12+x5+1) * * * * * * * * * * * *
* * 参数 1，uint8_t *data：需要计算的数据 * * * * * * * * * * *
* * 参数 1，uint16_t len：需要计算的数据字节长度 * * * * * * * *
* * 返回值，uint16_t crc16：计算出的 CRC 值 * * * * * * * * * * *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
unsigned short  crc_16(unsigned char *data, int len)
{
 unsigned short crc16 = 0xFFFF; //定义 CRC 计算的初始值
 unsigned short crc_high8, crc_low8;
 while( len-- ) {
 crc_high8 = (crc16 >> 8);
 crc_low8 = (crc16 << 8);
 crc16 = crc_low8 ^ crc_table[crc_high8 ^ *data];
 data++;
 }
 return crc16;
}
void main()
{
unsigned char data[13]={0x11,0x22,0x33,0x44,0x55,0x66,0x77,0x88,0x01,0x00,0x0d,0x12,0x34};
unsigned short crc;
crc=crc_16(data,13);
printf("0x%.2x",crc);

}

逻辑法
#include<stdio.h>
unsigned short UpdateCRC(unsigned char *CRC_input, unsigned int len)
{
    unsigned char i,k = 0;
    unsigned short CRC=0xffff;
    int j;
    #define POLY_  0x1021
    while (len--)
    //for (j = 0; j <13; j++)
    {
        CRC = CRC ^ (CRC_input[k++] << 8);//CRC异或为本身，crc为16bits   CRC_input[k] << 8为0x1100

        for (i = 0; i < 8; i++)
        {
            if ((CRC & 0x8000) == 0x8000)//判断高位是否为1
            {
             
                CRC = CRC << 1;//左移一位
               
                CRC ^= POLY_;//异或多项式
              
            }
            else
            {
               
                CRC = CRC << 1;//左移一位
               
            }
        }
    }
    return CRC;
}


int main(){
    unsigned short crc;
    unsigned char  buf_value[13] = {0x11,0x22,0x33,0x44,0x55,0x66,0x77,0x88,0x01,0x00,0x0d,0x12,0x34};
    int i;
    crc=UpdateCRC(buf_value,13);
    
    printf("%x\n",crc);
    
    return 0;
}