HCS412 Datasheet, PDF (33/44 Pages) Microchip Technology – KEELOQ Code Hopping Encoder and Transponder

FIGURE 6-3:
SYNCHRONIZATION WINDOW
Entire Window
rotates to eliminate
use of previously
used codes
Blocked
Window
(32K Codes)
Double Operation
(resynchronization)
Window
(32K Codes)
HCS412
Stored
Synchronization
Counter Value
Single Operation
Window
(16 Codes)
FIGURE 6-4:
BASIC OPERATION OF RECEIVER (DECODER)
1 Received Information
Button Press
Information
Serial Number
32 Bits of
Encrypted Data
EEPROM Array
Manufacturer Code
2
Check for
Match
3
KEELOQ
Decryption
Algorithm
Serial Number
Sync Counter
Crypt Key
Perform Function
5
Indicated by
button press
Decrypted
Synchronization
Counter
Note: Circled numbers indicate sequence of events.
4
Check for
Match
© 2002 Microchip Technology Inc.
Preliminary
DS41099C-page 33