crcmodbus.c

#include <stdio.h>
#include <stdint.h>

uint16_t crc16modbus(uint8_t *data, uint16_t len)
{
	uint16_t poly = 0xA001;
	uint16_t crc = 0xffff;
	uint8_t *ptr = data;

	while(len--)
	{
		crc ^= (0xFF & *ptr++);
		for (uint8_t i = 0 ; i < 8 ; i++)
		{
			if (crc & 0x0001)
				crc = ((crc >> 1)  & 0xFFFF) ^ poly;
			else
				crc = ((crc >> 1)  & 0xFFFF);
		}
	}
	return crc;
}

int main(int argc, char *argv[])
{
	uint8_t instr[]={0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39 };
	
	printf("CRC: 0x%04x\n", crc16modbus(instr, sizeof(instr)));

	return 0;
}