HCS201_11 Datasheet, PDF (6/36 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder 34-bit fixed code (28-bit serial number

HCS201
FIGURE 2-2:
ENCODER OPERATION
Power-Up
(A button has been pressed)
RESET and Debounce Delay
(10 ms)
Sample Inputs
Update Sync Info
Encrypt With
Crypt Key
Load Transmit Register
Transmit
Yes
Buttons
Added
?
No
All
No
Buttons
Released
?
Yes
Complete Code
Word Transmission
Stop
3.0 EEPROM MEMORY
ORGANIZATION
The HCS201 contains 192 bits (12 x 16-bit words) of
EEPROM memory (Table 3-1). This EEPROM array is
used to store the encryption key information, synchro-
nization value, etc. Further descriptions of the memory
array is given in the following sections.
TABLE 3-1: EEPROM MEMORY MAP
WORD
ADDRESS
0
1
2
3
4
5
6
7
8
9
10
11
MNEMONIC
DESCRIPTION
KEY_0
64-bit encryption key
(word 0)
KEY_1
64-bit encryption key
(word 1)
KEY_2
64-bit encryption key
(word 2)
KEY_3
64-bit encryption key
(word 3)
SYNC
16-bit synchronization
value
RESERVED Set to 0000H
SER_0
Device Serial Number
(word 0)
SER_1
Device Serial Number
(word 1)
SEED_0 Seed Value (word 0)
SEED_1 Seed Value (word 1)
DISC Discrimination Word
CONFIG Config Word
3.1 KEY_0 - KEY_3 (64-Bit Crypt Key)
The 64-bit crypt key is used to create the encrypted
message transmitted to the receiver. This key is calcu-
lated and programmed during production using a key
generation algorithm. The key generation algorithm
may be different from the KEELOQ algorithm. Inputs to
the key generation algorithm are typically the transmit-
ter’s serial number and the 64-bit manufacturer’s code.
While the key generation algorithm supplied from
Microchip is the typical method used, a user may elect
to create their own method of key generation. This may
be done providing that the decoder is programmed with
the same means of creating the key for
decryption purposes.
3.2 SYNC (Synchronization Counter)
This is the 16-bit synchronization value that is used to
create the hopping code for transmission. This value
will increment after every transmission.
DS41098D-page 6
© 2011 Microchip Technology Inc.