CRC iButton'a

Hello, Valentin! You wrote to All on Wed, 14 Sep 2005 23:05:20 +0400:

VM> çÏÓÐÏÄÁ, pÁÓÛÉÆpÕÊÔÅ ÍÎÅ ÐÌÉÚ ÁÌÇÏpÉÔÍ ÐÏÄÓÞÅÔÁ CRC Õ ÜÔÏÇÏ iButton'a. ÷ÓÀ VM> ÇÏÌÏ×Õ ÓÌÏÍÁÌ ÕÖÅ. íÎÅ ÎÁ á÷ò ÎÁÄÏ. ðÅpÅÐÉÓÁÌ Ó 51ÇÏ, ÆÉÇ pÁÂÏÔÁÅÔ, × ÔÏÍ VM> ÓÍÙÓÌÅ, ÞÔÏ ÎÅ ÎÏÌØ × ÓÕÍÍÅ.

á ÞÅÇÏ ÔÁÍ ÒÁÓÛÉÆÒÏ×Ù×ÁÔØ? äÅÒÖÉ ÎÁ ãÅ (Data[0..7] - ÍÁÓÓÉ× ÐÒÉÎÑÔÙÈ ÄÁÎÎÙÈ)

char a=0; char b, z; //ÐÒÏ×ÅÒËÁ CRC for(z=0;z= 1; a |= 0x80; } else a >>= 1; temp >>= 1; } } if(a) { //ÎÅÐÒÁ×ÉÌØÎÙÊ CRC }

éÍÅÊ × ×ÉÄÕ, ÞÔÏ ÖÅÌÁÔÅÌØÎÏ ÅÝÅ ×ÅÓØ ÍÁÓÓÉ× ÎÁ ÒÁ×ÅÎÓÔ×Ï 0 ÐÒÏ×ÅÒÑÔØ, É ÏÔÂÒÁÓÙ×ÁÔØ, ÅÓÌÉ ÔÁË. éÂÏ × ÓÉÌÕ ÏÓÏÂÅÎÎÏÓÔÅÊ ÒÅÁÌÉÚÁÃÉÉ CRC ÏÔ Dallas ÐÏÌÎÏÓÔØÀ ÎÕÌÅ×ÏÊ ÍÁÓÓÉ× ÓÞÉÔÁÅÔÓÑ ×ÅÒÎÙÍ.

With best regards, Sergey Zabelin. E-mail: snipped-for-privacy@telemak.ru

Hi Valentin!

14 ÓÅÎÔÑÂÒÑ 2005 23:05, Valentin Monokonoff ÐÉÓÁÌ All:

VM> ëÁÔÅÇÏÒÉÞÅÓËÉ ÐÒÉ×ÅÔÓÔ×ÕÀ ÷ÁÓ, Õ×ÁÖÁÅÍÙÊ All!

VM> çÏÓÐÏÄÁ, pÁÓÛÉÆpÕÊÔÅ ÍÎÅ ÐÌÉÚ ÁÌÇÏpÉÔÍ ÐÏÄÓÞÅÔÁ CRC Õ ÜÔÏÇÏ VM> iButton'a. ÷ÓÀ ÇÏÌÏ×Õ ÓÌÏÍÁÌ ÕÖÅ. íÎÅ ÎÁ á÷ò ÎÁÄÏ. ðÅpÅÐÉÓÁÌ Ó 51ÇÏ, VM> ÆÉÇ pÁÂÏÔÁÅÔ, × ÔÏÍ ÓÍÙÓÌÅ, ÞÔÏ ÎÅ ÎÏÌØ × ÓÕÍÍÅ.

#include "crc.h" unsigned char calculate_crc8(unsigned char* data_pointer, unsigned char number_of_bytes) { unsigned char temp1=0, bit_counter=0, feedback_bit=0, crc8_result=0;

while(number_of_bytes--) { temp1=(*(data_pointer++));

for(bit_counter=8; bit_counter; bit_counter--) { feedback_bit=(crc8_result & 0x01); crc8_result=(crc8_result >> 1); if(feedback_bit ^ (temp1 & 0x01)) { crc8_result=(crc8_result ^ 0x8c); } temp1=(temp1 >> 1); }

}

return(crc8_result); }

/* crc array from the Maxim ApNote

*/

const unsigned char crc_array[256] = {

0x00, 0x5e, 0xbc, 0xe2, 0x61, 0x3f, 0xdd, 0x83, 0xc2, 0x9c, 0x7e, 0x20, 0xa3, 0xfd, 0x1f, 0x41, 0x9d, 0xc3, 0x21, 0x7f, 0xfc, 0xa2, 0x40, 0x1e, 0x5f, 0x01, 0xe3, 0xbd, 0x3e, 0x60, 0x82, 0xdc, 0x23, 0x7d, 0x9f, 0xc1, 0x42, 0x1c, 0xfe, 0xa0, 0xe1, 0xbf, 0x5d, 0x03, 0x80, 0xde, 0x3c, 0x62, 0xbe, 0xe0, 0x02, 0x5c, 0xdf, 0x81, 0x63, 0x3d, 0x7c, 0x22, 0xc0, 0x9e, 0x1d, 0x43, 0xa1, 0xff, 0x46, 0x18, 0xfa, 0xa4, 0x27, 0x79, 0x9b, 0xc5, 0x84, 0xda, 0x38, 0x66, 0xe5, 0xbb, 0x59, 0x07, 0xdb, 0x85, 0x67, 0x39, 0xba, 0xe4, 0x06, 0x58, 0x19, 0x47, 0xa5, 0xfb, 0x78, 0x26, 0xc4, 0x9a, 0x65, 0x3b, 0xd9, 0x87, 0x04, 0x5a, 0xb8, 0xe6, 0xa7, 0xf9, 0x1b, 0x45, 0xc6, 0x98, 0x7a, 0x24, 0xf8, 0xa6, 0x44, 0x1a, 0x99, 0xc7, 0x25, 0x7b, 0x3a, 0x64, 0x86, 0xd8, 0x5b, 0x05, 0xe7, 0xb9, 0x8c, 0xd2, 0x30, 0x6e, 0xed, 0xb3, 0x51, 0x0f, 0x4e, 0x10, 0xf2, 0xac, 0x2f, 0x71, 0x93, 0xcd, 0x11, 0x4f, 0xad, 0xf3, 0x70, 0x2e, 0xcc, 0x92, 0xd3, 0x8d, 0x6f, 0x31, 0xb2, 0xec, 0x0e, 0x50, 0xaf, 0xf1, 0x13, 0x4d, 0xce, 0x90, 0x72, 0x2c, 0x6d, 0x33, 0xd1, 0x8f, 0x0c, 0x52, 0xb0, 0xee, 0x32, 0x6c, 0x8e, 0xd0, 0x53, 0x0d, 0xef, 0xb1, 0xf0, 0xae, 0x4c, 0x12, 0x91, 0xcf, 0x2d, 0x73, 0xca, 0x94, 0x76, 0x28, 0xab, 0xf5, 0x17, 0x49, 0x08, 0x56, 0xb4, 0xea, 0x69, 0x37, 0xd5, 0x8b, 0x57, 0x09, 0xeb, 0xb5, 0x36, 0x68, 0x8a, 0xd4, 0x95, 0xcb, 0x29, 0x77, 0xf4, 0xaa, 0x48, 0x16, 0xe9, 0xb7, 0x55, 0x0b, 0x88, 0xd6, 0x34, 0x6a, 0x2b, 0x75, 0x97, 0xc9, 0x4a, 0x14, 0xf6, 0xa8, 0x74, 0x2a, 0xc8, 0x96, 0x15, 0x4b, 0xa9, 0xf7, 0xb6, 0xe8, 0x0a, 0x54, 0xd7, 0x89, 0x6b, 0x35, };

unsigned char crc8_table (unsigned char *pData, int count, unsigned char crc) { while (count--) { crc = crc_array[*pData ^ crc]; pData++; } return crc; } unsigned char crc8_table_byte (unsigned char data, unsigned char crc) { return crc_array [data ^ crc]; } Bye Valentin! ... á ÔÙ ×ÏÓÐÏÌØÚÏ×ÁÌÓÑ ÐÁËÅÔÏÍ FTN?

Hello, Dimmy Timchenko! You wrote in conference fido7.ru.embedded to Alexy Gorbach on Tue, 11 Oct 2005 05:16:17

+0400:

DT> Кстати, о стиле...

AG>> for(bit_counter=8; bit_counter; bit_counter--)

DT> Я б обязательно написал bit_counter > 0;

Какая разница?

AG>> crc8_result=(crc8_result >> 1);

DT> А здесь как раз хорошо подходит "операция присваивания":

DT> crc8_result >>= 1;

Ага.

dima