PIC单片机CRC校验程序

1、pic单片机crc校验程序用和dallas的ibutton通讯时，编了段产生和校验crc的子程序。include;-cblock 0x20datbuff:8 ;assign 8 byte data bufferbit_cnt ;bit countingcrc_count ;number of bytes for crccrc_result ;crc resulrcrc_temp ;temporary data buffer during crcendc;-define skp0 btfscdefine skp1 btfss;=org 0x000movlw .7movwf crc_countmo

2、vlw datbuffmovwf fsr ;fsr point to data buffercall crc_checkmovwf datbuff+7goto $;=;check the crc for ? bytes data;for the polynomial of x8 + x5 + x4 + 1;derived from dallas's ibutton standard;before calling, fsr = data buffer; crc_count = number of bytes for crccrc_check ;"""&quo

3、t;"""""""""""clrf crc_result ;initialize the crc buffer_crc_00movlw .8 ;number of bits for one bytemovwf bit_cnt ;set bit countermovf indf,w ;get one data bytemovwf crc_temp ;copy to temporary location_crc_01rrf crc_temp,f ;get lsb in cskpc ;is

4、this lsb=1?goto _crc_02 ;go if lsb=0movlw 0x01 ;do if lsb=1xorwf crc_result,f_crc_02rrf crc_result,w ;get lsb of crcskpc ;test lsbgoto _crc_03 ;go if lsb=0movlw 0x18 ;do if lsb=1xorwf crc_result,f ;polynomial implementation_crc_03rrf crc_result,w ;whole byte right rotaterrf crc_result,fdecfsz bit_cnt,f ;bit countinggoto _crc_01 ;go on until aa 8 bits doneincf fsr,f ;pointer update to next bytedecfsz crc_count,f ;byte countinggoto _crc_00 ;go on until all byte donemovf crc_res