Steve Spence / Mbed 2 deprecated DS18B20Sensor

Simple cpp wrapper of a ds18b20, onewire 'c' library. Supports multiple sensors.

Dependencies:   mbed

Dependents:   DS18B20Sensor DS18B201

crc8.cpp@3:9fd95d590149, 2013-03-03 (annotated)

Committer:
jsteve
Date:
Sun Mar 03 02:22:27 2013 +0000
Revision:
3:9fd95d590149
Parent:
0:1449f126b241 
Updated documentation.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
jsteve 0:1449f126b241 1 #include <inttypes.h>
jsteve 0:1449f126b241 2
jsteve 0:1449f126b241 3 #define CRC8INIT 0x00
jsteve 0:1449f126b241 4 #define CRC8POLY 0x18 //0X18 = X^8+X^5+X^4+X^0
jsteve 0:1449f126b241 5
jsteve 0:1449f126b241 6 uint8_t crc8 ( uint8_t *data_in, uint16_t number_of_bytes_to_read )
jsteve 0:1449f126b241 7 {
jsteve 0:1449f126b241 8 uint8_t crc;
jsteve 0:1449f126b241 9 uint16_t loop_count;
jsteve 0:1449f126b241 10 uint8_t bit_counter;
jsteve 0:1449f126b241 11 uint8_t data;
jsteve 0:1449f126b241 12 uint8_t feedback_bit;
jsteve 0:1449f126b241 13
jsteve 0:1449f126b241 14 crc = CRC8INIT;
jsteve 0:1449f126b241 15
jsteve 0:1449f126b241 16 for (loop_count = 0; loop_count != number_of_bytes_to_read; loop_count++)
jsteve 0:1449f126b241 17 {
jsteve 0:1449f126b241 18 data = data_in[loop_count];
jsteve 0:1449f126b241 19
jsteve 0:1449f126b241 20 bit_counter = 8;
jsteve 0:1449f126b241 21 do {
jsteve 0:1449f126b241 22 feedback_bit = (crc ^ data) & 0x01;
jsteve 0:1449f126b241 23
jsteve 0:1449f126b241 24 if ( feedback_bit == 0x01 ) {
jsteve 0:1449f126b241 25 crc = crc ^ CRC8POLY;
jsteve 0:1449f126b241 26 }
jsteve 0:1449f126b241 27 crc = (crc >> 1) & 0x7F;
jsteve 0:1449f126b241 28 if ( feedback_bit == 0x01 ) {
jsteve 0:1449f126b241 29 crc = crc | 0x80;
jsteve 0:1449f126b241 30 }
jsteve 0:1449f126b241 31
jsteve 0:1449f126b241 32 data = data >> 1;
jsteve 0:1449f126b241 33 bit_counter--;
jsteve 0:1449f126b241 34
jsteve 0:1449f126b241 35 } while (bit_counter > 0);
jsteve 0:1449f126b241 36 }
jsteve 0:1449f126b241 37
jsteve 0:1449f126b241 38 return crc;
jsteve 0:1449f126b241 39 }