RFHCS362F Datasheet, PDF(16/60 Page) Microchip Technology – Code Hopping Encoder with UHF ASK/FSK Transmitter

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RFHCS362F Datasheet, PDF (16/60 Pages) Microchip Technology – Code Hopping Encoder with UHF ASK/FSK Transmitter

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rfHCS362G/362F

3.1.4.4 Cyclic Redundancy Check (CRC)

The CRC bits are calculated on the 65 previously trans-

mitted bits. The decoder can use the CRC bits to check

the data integrity before processing starts. The CRC

can detect all single bit errors and 66% of double bit

errors. The CRC is computed as follows:

EQUATION 3-1: CRC Calculation

CRC[1]n + 1 = CRC[0]n â Din

and

CRC[0]n + 1 = (CRC[0]n â Din) â CRC[1]n

with

CRC[1, 0]0 = 0

and Din the nth transmission bit 0 â¤ n â¤ 64

Warning: The CRC may be wrong when the battery

voltage is near the selected VLOW trip point.

This may happen because VLOW is sam-

pled twice each transmission, once for the

CRC calculation and once when VLOW is

transmitted. VDD tends to move slightly dur-

ing a transmission which could lead to a dif-

ferent value for VLOW being used for the

CRC calculation and the transmission.

Work around: If the CRC is incorrect,

recalculate for the opposite value of VLOW.

DS41189A-page 16

Preliminary

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