HCS515 Просмотр технического описания (PDF) - Microchip Technology

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HCS515

KEELOQ Code Hopping Decoder

Microchip Technology 

HCS515

1.3 HCS Decoder Overview

Before a transmitter and receiver can work together,

the receiver must first ‘learn’ and store certain informa-

tion from the transmitter. This information includes a

‘check value’ of the serial number, the encoder decryp-

tion key, and current synchronization counter value.

When a valid formatted message is detected, the

receiver first compares the serial number. If the serial

number check value is from a learned transmitter, the

message is decrypted. Next, the receiver checks the

decrypted synchronization counter value against what

is stored in memory. If the synchronization counter

value is verified, then a valid transmission message is

sent. Figure 1-3 shows the relationship between some

of the values stored by the receiver and the values

received from the transmitter.

FIGURE 1-2: BASIC OPERATION OF A CODE HOPPING TRANSMITTER (ENCODER)

Transmitted Information

EEPROM Array

Encoder Decryption Key

Sync. Counter Value

Serial Number

KEELOQ

Encryption

Algorithm

32 Bits of

Encrypted Data

Serial Number

Button Press

Information

FIGURE 1-3: BASIC OPERATION OF A CODE HOPPING RECEIVER (DECODER)

EEPROM Array

Encoder Decryption Key

Sync. Counter Value

Serial Number

Manufacturer Code

Check for

Match

KEELOQ

Decryption

Algorithm

Check for

Match

Decrypted

Synchronization

Counter

Button Press

Information

Serial Number

32 Bits of

Encrypted Data

Received Information

© 1998 Microchip Technology Inc.

Preliminary

DS40183A-page 3

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