frederic blanc / OneWire_II

MAX31850, DS18B20, DS2450, thermocouple

crc8.cpp@0:5d39f2521173, 2015-03-09 (annotated)

Committer:
fblanc
Date:
Mon Mar 09 11:55:54 2015 +0000
Revision:
0:5d39f2521173
MAX31850

Who changed what in which revision?

UserRevisionLine numberNew contents of line
fblanc 0:5d39f2521173 1 #include <inttypes.h>
fblanc 0:5d39f2521173 2
fblanc 0:5d39f2521173 3 #define CRC8INIT 0x00
fblanc 0:5d39f2521173 4 #define CRC8POLY 0x18 //0X18 = X^8+X^5+X^4+X^0
fblanc 0:5d39f2521173 5
fblanc 0:5d39f2521173 6 uint8_t crc8 ( uint8_t *data_in, uint16_t number_of_bytes_to_read )
fblanc 0:5d39f2521173 7 {
fblanc 0:5d39f2521173 8 uint8_t crc;
fblanc 0:5d39f2521173 9 uint16_t loop_count;
fblanc 0:5d39f2521173 10 uint8_t bit_counter;
fblanc 0:5d39f2521173 11 uint8_t data;
fblanc 0:5d39f2521173 12 uint8_t feedback_bit;
fblanc 0:5d39f2521173 13
fblanc 0:5d39f2521173 14 crc = CRC8INIT;
fblanc 0:5d39f2521173 15
fblanc 0:5d39f2521173 16 for (loop_count = 0; loop_count != number_of_bytes_to_read; loop_count++)
fblanc 0:5d39f2521173 17 {
fblanc 0:5d39f2521173 18 data = data_in[loop_count];
fblanc 0:5d39f2521173 19
fblanc 0:5d39f2521173 20 bit_counter = 8;
fblanc 0:5d39f2521173 21 do {
fblanc 0:5d39f2521173 22 feedback_bit = (crc ^ data) & 0x01;
fblanc 0:5d39f2521173 23
fblanc 0:5d39f2521173 24 if ( feedback_bit == 0x01 ) {
fblanc 0:5d39f2521173 25 crc = crc ^ CRC8POLY;
fblanc 0:5d39f2521173 26 }
fblanc 0:5d39f2521173 27 crc = (crc >> 1) & 0x7F;
fblanc 0:5d39f2521173 28 if ( feedback_bit == 0x01 ) {
fblanc 0:5d39f2521173 29 crc = crc | 0x80;
fblanc 0:5d39f2521173 30 }
fblanc 0:5d39f2521173 31
fblanc 0:5d39f2521173 32 data = data >> 1;
fblanc 0:5d39f2521173 33 bit_counter--;
fblanc 0:5d39f2521173 34
fblanc 0:5d39f2521173 35 } while (bit_counter > 0);
fblanc 0:5d39f2521173 36 }
fblanc 0:5d39f2521173 37
fblanc 0:5d39f2521173 38 return crc;
fblanc 0:5d39f2521173 39 }