https://blog.csdn.net/u013625451/article/details/81239572

http://cht.nahua.com.tw/index.php?url=http://cht.nahua.com.tw/software/crc16/&key=Modbus,%20RTU,%20CRC16&title=%E8%A8%88%E7%AE%97%20Modbus%20RTU%20CRC16

void main(void)
{
	unsigned short tmp = 0xffff;
	unsigned short ret1 = 0;
	unsigned char buff[4] = { 0 };
	buff[0] = 0xB1;
	buff[1] = 0x00;
	buff[2] = 0x00;
	buff[3] = 0x01;

	for (int n = 0; n < 4; n++) {/*此處的6 -- 要校驗的位數為6個*/
		tmp = buff[n] ^ tmp;
		for (int i = 0; i < 8; i++) {  /*此處的8 -- 指每一個char型別又8bit，每bit都要處理*/
			if (tmp & 0x01) {
				tmp = tmp >> 1;
				tmp = tmp ^ 0xa001;
			}
			else {
				tmp = tmp >> 1;
			}
		}
	}
	/*CRC校驗後的值*/
	printf("%X\n", tmp);
	/*將CRC校驗的高低位對換位置*/
	ret1 = tmp >> 8;
	ret1 = ret1 | (tmp << 8);
	printf("ret: %X\n", ret1);
	return 0;

}