HCS361-IP datasheet(3/24 Pages) MICROCHIP

3 / 24 page

HCS361

Preliminary

DS40146C-page 3

Before a transmitter can be used with a particular

receiver, the transmitter must be ‘learned’ by the

receiver. Upon learning a transmitter, information is

stored by the receiver so that it may track the

transmitter,

including

the

serial

number

the

transmitter, the current synchronization value for that

transmitter and the same encryption key that is used on

the transmitter. If a receiver receives a message of valid

format, the serial number is checked and, if it is from a

learned transmitter, the message is decrypted and the

decrypted synchronization counter is checked against

what is stored. If the synchronization value is veriﬁed,

then the button status is checked to see what operation

is needed. Figure 1-3 shows the relationship between

some of the values stored by the receiver and the val-

ues received from the transmitter.

FIGURE 1-1:

CREATION AND STORAGE OF ENCRYPTION KEY DURING PRODUCTION

FIGURE 1-2:

BASIC OPERATION OF TRANSMITTER (ENCODER)

FIGURE 1-3:

BASIC OPERATION OF RECEIVER (DECODER)

Transmitter

Manufacturer’s

Serial Number or

Code

Encryption

Key

Generation

Algorithm

Serial Number

Encryption Key

Sync Counter

HCS361 EEPROM Array

Seed

KEELOQ

Algorithm

Button Press

Information

Encryption

EEPROM Array

32 Bits of

Encrypted Data

Serial Number

Transmitted Information

Decryption Key

Sync Counter

Serial Number

Button Press

Information

EEPROM Array

Decryption Key

32 Bits of

Encrypted Data

Serial Number

Received Information

Decrypted

Synchronization

Counter

Check for

Match

Check for

Match

KEELOQ

Algorithm

Decryption

Sync Counter

Serial Number

Manufacturer Code

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