MCS3142-ISLASHST datasheet(8/37 Pages) MICROCHIP

部品番号	MCS3142-I/ST

部品情報	MCS3142 Dual KEELOQ짰 Technology Encoder Data Sheet

PDF	37 Pages

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メーカー	MICROCHIP [Microchip Technology]

ホームページ	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;

}

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