HCS512 datasheet(7/34 Pages) MICROCHIP

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DS40151E-page 7

HCS512

4.2

Validation of Codes

The decoder waits for a transmission and checks the

serial number to determine if the transmitter has been

learned. If learned, the decoder decrypts the encrypted

portion of the transmission using the crypt key. It uses

the discrimination bits to determine if the decryption

was valid. If everything up to this point is valid, the

synchronization value is evaluated.

4.3

Validation Steps

Validation consists of the following steps:

• Search EEPROM to find the Serial Number

Check Value Match

• Decrypt the Hopping Code

• Compare the 10 bits of discrimination value with

the lower 10 bits of serial number

• Check if the synchronization counter falls within

the first synchronization window.

• Check if the synchronization counter falls within

the second synchronization window.

• If a valid transmission is found, update the syn-

chronization counter, else use the next transmitter

block and repeat the tests.

FIGURE 4-2:

DECODER OPERATION

Transmission

Received

Does

Ser # Check Val

Match

Decrypt Transmission

Decryption

Valid

Counter

Within 16

Counter

Within 32K

Update

Counter

Execute

Command

Save Counter

in Temp Location

Start

Yes

and

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