hcs512 Microchip Technology Inc., hcs512 Datasheet - Page 7

• Manufacturer Part Number: hcs512
• Description: Keeloq Code Hopping Decoder Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

4.2
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 consists of the following steps:
• Search EEPROM to find the Serial Number
• Decrypt the Hopping Code
• Compare the 10 bits of discrimination value with
• Check if the synchronization counter falls within
• Check if the synchronization counter falls within
• If a valid transmission is found, update the syn-
Check Value Match
the lower 10 bits of serial number
the first synchronization window.
the second synchronization window.
chronization counter, else use the next transmitter
block and repeat the tests.
2002 Microchip Technology Inc.
Validation of Codes
Validation Steps
FIGURE 4-2:
No
No
No
No
Decrypt Transmission
in Temp Location
Ser # Check Val
Save Counter
Transmission
Within 32K
Decryption
Within 16
Received
Counter
Counter
Match
Does
Valid
Start
Is
Is
Is
?
?
?
DECODER OPERATION
?
?
Yes
Yes
Yes
Yes
No
Yes
HCS512
Command
Execute
Counter
Update
DS40151D-page 7
and