HCS320_11 Datasheet, PDF (6/38 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder Automatic code word completion

HCS320
FIGURE 2-2:
ENCODER OPERATION
Power-Up
(Button pressed) Set TX:= OFF
RESET and Debounce Delay
(10 ms)
Transmit
Button Pressed? ^Yes
No
Increment Shift Level
Set TX:=ON
Stop Transmit
No
Shift
Button Pressed?
Yes
Yes
TX=ON?
Yes
Update Sync Info
Encrypt With
Crypt Key
No
Load Transmit Register
Transmit
Buttons
Added?
No
No
All
Buttons
Released?
Yes
TX=ON?
Yes
Complete Code
Word Transmission
No
Stop
3.0 EEPROM MEMORY
ORGANIZATION
The HCS320 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) LSb’s
1
KEY_1 64-bit encryption key
(word 1)
2
3
4
5
6
7
8
9
10
11
Note:
KEY_2
64-bit encryption key
(word 2)
KEY_3
64-bit encryption key
(word 3) MSb’s
SYNC
16-bit synchronization
value
RESERVED Set to 0000H
SER_0
Device Serial Number
(word 0) LSb’s
SER_1(Note) Device Serial Number
(word 1) MSb’s
—
Not used
—
Not used
RESERVED Set to 0000H
CONFIG Configuration Word
The MSB of the serial number contains a
bit used to select the Auto-shutoff timer.
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.
DS41097D-page 6
© 2011 Microchip Technology Inc.