MCS3142_14 datasheet(8/37 Pages) MICROCHIP

Numer części	MCS3142

Szczegółowy opis	MCS3142 Dual KEELOQ짰 Technology Encoder Data Sheet

PDF	37 Pages

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Producent	MICROCHIP [Microchip Technology]

Strona internetowa	http://www.microchip.com

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MCS3142

DS40001747A-page 8

 2014 Microchip Technology Inc.

3.1

Counter and Timer Protection

Because they are written during normal operation of

the device, the two synchronization counters, Reset

counter and time value receive special protection to

guard against data loss from unexpected power loss.

An 8-bit CRC is calculated and stored alongside each

variable. Further, each variable is duplicated in a

different portion of memory. Whenever a value is read,

the CRC is calculated and verified against the stored

value. If there is a mismatch, the second copy of the

data is read instead. The CRC calculation uses a

polynomial

represented

Example 3-1 describes a sample C function to compute

this value.

EXAMPLE 3-1:

CRC CALCULATION

++++

static uint8_t crc(const uint8_t* buffer, size_t len){

uint8_t bitcount;

uint8_t c = 0xFF;

while(len--)

{

c ^= *buffer++;

for(bitcount = 0; bitcount < 8; bitcount++){

if((c & 0x80)!= 0) {

c <<= 1;

c ^= 0x1D;

}else{

c <<= 1;

}

return ~c;

}

MCS3142 Arkusz danych(PDF) 8 Page - Microchip Technology