frederic blanc / Mbed 2 deprecated OneWireDrv

onewire DS18B20 DS2450

Dependencies:   mbed

crc8.cpp@0:df0e3c8895f4, 2011-06-30 (annotated)

Committer:
fblanc
Date:
Thu Jun 30 13:18:22 2011 +0000
Revision:
0:df0e3c8895f4
2011_06_30

Who changed what in which revision?

UserRevisionLine numberNew contents of line
fblanc 0:df0e3c8895f4 1 #include <inttypes.h>
fblanc 0:df0e3c8895f4 2
fblanc 0:df0e3c8895f4 3 #define CRC8INIT 0x00
fblanc 0:df0e3c8895f4 4 #define CRC8POLY 0x18 //0X18 = X^8+X^5+X^4+X^0
fblanc 0:df0e3c8895f4 5
fblanc 0:df0e3c8895f4 6 uint8_t crc8 ( uint8_t *data_in, uint16_t number_of_bytes_to_read )
fblanc 0:df0e3c8895f4 7 {
fblanc 0:df0e3c8895f4 8 uint8_t crc;
fblanc 0:df0e3c8895f4 9 uint16_t loop_count;
fblanc 0:df0e3c8895f4 10 uint8_t bit_counter;
fblanc 0:df0e3c8895f4 11 uint8_t data;
fblanc 0:df0e3c8895f4 12 uint8_t feedback_bit;
fblanc 0:df0e3c8895f4 13
fblanc 0:df0e3c8895f4 14 crc = CRC8INIT;
fblanc 0:df0e3c8895f4 15
fblanc 0:df0e3c8895f4 16 for (loop_count = 0; loop_count != number_of_bytes_to_read; loop_count++)
fblanc 0:df0e3c8895f4 17 {
fblanc 0:df0e3c8895f4 18 data = data_in[loop_count];
fblanc 0:df0e3c8895f4 19
fblanc 0:df0e3c8895f4 20 bit_counter = 8;
fblanc 0:df0e3c8895f4 21 do {
fblanc 0:df0e3c8895f4 22 feedback_bit = (crc ^ data) & 0x01;
fblanc 0:df0e3c8895f4 23
fblanc 0:df0e3c8895f4 24 if ( feedback_bit == 0x01 ) {
fblanc 0:df0e3c8895f4 25 crc = crc ^ CRC8POLY;
fblanc 0:df0e3c8895f4 26 }
fblanc 0:df0e3c8895f4 27 crc = (crc >> 1) & 0x7F;
fblanc 0:df0e3c8895f4 28 if ( feedback_bit == 0x01 ) {
fblanc 0:df0e3c8895f4 29 crc = crc | 0x80;
fblanc 0:df0e3c8895f4 30 }
fblanc 0:df0e3c8895f4 31
fblanc 0:df0e3c8895f4 32 data = data >> 1;
fblanc 0:df0e3c8895f4 33 bit_counter--;
fblanc 0:df0e3c8895f4 34
fblanc 0:df0e3c8895f4 35 } while (bit_counter > 0);
fblanc 0:df0e3c8895f4 36 }
fblanc 0:df0e3c8895f4 37
fblanc 0:df0e3c8895f4 38 return crc;
fblanc 0:df0e3c8895f4 39 }