HCS201 datasheet(6/28 Pages) MICROCHIP

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HCS201

DS41098C-page 6

FIGURE 2-2:

ENCODER OPERATION

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

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

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.

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

Yes

Crypt Key

Complete Code

Word Transmission

WORD

ADDRESS

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

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