HCS360 Datasheet, PDF (5/24 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER

FIGURE 2-2:
ENCODER OPERATION
Power Up
(A button has been pressed)
Reset and Debounce Delay
(6.5 ms)
Sample Inputs
Update Sync Info
Encrypt With
Encryption Key
Load Transmit Register
Transmit
Yes
Buttons
Added
?
No
All
No
Buttons
Released
?
Yes
Complete Code
Word Transmission
Stop
HCS360
3.0 EEPROM MEMORY
ORGANIZATION
The HCS360 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,
synchronization value, etc. Further descriptions of the
memory array is given in the following sections.
TABLE 3-1 EEPROM MEMORY MAP
WORD
ADDRESS
MNEMONIC
DESCRIPTION
0
KEY_0
64-bit encryption
key (word 0)
1
KEY_1
64-bit encryption
key (word 1)
2
KEY_2
64-bit encryption
key (word 2)
3
KEY_3
64-bit encryption
key (word 3)
4
SYNC_A
16-bit synchroniza-
tion value
5
SYNC_B/SEED_2 16-bit synchroniza-
tion or seed value
(word 2)
6
RESERVED Set to 0000H
7
SEED_0
Seed Value (word 0)
8
SEED_1
Seed Value (word 1)
7
SER_0
Device Serial
Number (word 0)
10
SER_1
Device Serial
Number (word 1)
11
CONFIG
Configuration Word
3.1 Key_0 - Key_3 (64-Bit Encryption Key)
The 64-bit encryption key is used by the transmitter to
create the encrypted message transmitted to the
receiver. This key is created and programmed at the
time of production using a key generation algorithm.
Inputs to the key generation algorithm are the serial
number for the particular transmitter being used and a
secret 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 creat-
ing the key for decryption purposes. If a seed is used,
the seed will also form part of the input to the key gen-
eration algorithm.
© 1996 Microchip Technology Inc.
Preliminary
DS40152C-page 5