frederic blanc / OneWireFB

OneWire DS18B20,DS2450,MAX31850

Dependents:   MAX31850_HelloWorld

crc8.cpp@0:9acbbb021a43, 2015-02-12 (annotated)

Committer:
fblanc
Date:
Thu Feb 12 14:03:55 2015 +0000
Revision:
0:9acbbb021a43
MAX31850 ok

Who changed what in which revision?

UserRevisionLine numberNew contents of line
fblanc 0:9acbbb021a43 1 #include <inttypes.h>
fblanc 0:9acbbb021a43 2
fblanc 0:9acbbb021a43 3 #define CRC8INIT 0x00
fblanc 0:9acbbb021a43 4 #define CRC8POLY 0x18 //0X18 = X^8+X^5+X^4+X^0
fblanc 0:9acbbb021a43 5
fblanc 0:9acbbb021a43 6 uint8_t crc8 ( uint8_t *data_in, uint16_t number_of_bytes_to_read )
fblanc 0:9acbbb021a43 7 {
fblanc 0:9acbbb021a43 8 uint8_t crc;
fblanc 0:9acbbb021a43 9 uint16_t loop_count;
fblanc 0:9acbbb021a43 10 uint8_t bit_counter;
fblanc 0:9acbbb021a43 11 uint8_t data;
fblanc 0:9acbbb021a43 12 uint8_t feedback_bit;
fblanc 0:9acbbb021a43 13
fblanc 0:9acbbb021a43 14 crc = CRC8INIT;
fblanc 0:9acbbb021a43 15
fblanc 0:9acbbb021a43 16 for (loop_count = 0; loop_count != number_of_bytes_to_read; loop_count++)
fblanc 0:9acbbb021a43 17 {
fblanc 0:9acbbb021a43 18 data = data_in[loop_count];
fblanc 0:9acbbb021a43 19
fblanc 0:9acbbb021a43 20 bit_counter = 8;
fblanc 0:9acbbb021a43 21 do {
fblanc 0:9acbbb021a43 22 feedback_bit = (crc ^ data) & 0x01;
fblanc 0:9acbbb021a43 23
fblanc 0:9acbbb021a43 24 if ( feedback_bit == 0x01 ) {
fblanc 0:9acbbb021a43 25 crc = crc ^ CRC8POLY;
fblanc 0:9acbbb021a43 26 }
fblanc 0:9acbbb021a43 27 crc = (crc >> 1) & 0x7F;
fblanc 0:9acbbb021a43 28 if ( feedback_bit == 0x01 ) {
fblanc 0:9acbbb021a43 29 crc = crc | 0x80;
fblanc 0:9acbbb021a43 30 }
fblanc 0:9acbbb021a43 31
fblanc 0:9acbbb021a43 32 data = data >> 1;
fblanc 0:9acbbb021a43 33 bit_counter--;
fblanc 0:9acbbb021a43 34
fblanc 0:9acbbb021a43 35 } while (bit_counter > 0);
fblanc 0:9acbbb021a43 36 }
fblanc 0:9acbbb021a43 37
fblanc 0:9acbbb021a43 38 return crc;
fblanc 0:9acbbb021a43 39 }