HCS300
DS21137E-page 6
Preliminary
1999 Microchip Technology Inc.
FIGURE 2-2:
ENCODER OPERATION
3.0
EEPROM MEMORY
ORGANIZATION
The HCS300 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
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 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 pro-
grammed with the same means of creating the key for
decryption purposes. If a seed is used, the seed will
also form part of the input to the key generation algo-
rithm.
Power Up
Reset and Debounce Delay
(10 ms)
Sample Inputs
Update Sync Info
Encrypt With
Load Transmit Register
Buttons
Added
?
All
Buttons
Released
?
(A button has been pressed)
Transmit
Stop
No
Yes
No
Yes
Encryption Key
Complete Code
Word Transmission
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
16-bit synchronization
value
5
RESERVED
Set to 0000H
6
SER_0
Device Serial Number
(word 0)
7
SER_1(Note) Device Serial Number
(word 1)
8
SEED_0
Seed Value (word 0)
9
SEED_1
Seed Value (word 1)
10
EN_KEY
16-bit Envelope Key
11
CONFIG
Config Word
Note:
The MSB of the serial number contains a bit
used to select the auto shutoff timer.
21137e.Book Page 6 Monday, October 4, 1999 8:04 AM
