HCS361 datasheet(6/42 Pages) MICROCHIP

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HCS361

DS40146F-page 6

3.0

EEPROM MEMORY

ORGANIZATION

The HCS361 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 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_A, SYNC_B

(Synchronization Counter)

This is the 16-bit synchronization value that is used to

create the hopping code for transmission. This value is

incremented after every transmission. Separate syn-

chronization counters can be used to stay synchro-

nized with different receivers.

3.3

SEED_0, SEED_1, and SEED_2

(Seed Word)

The three word (48 bits) seed code will be transmitted

when seed transmission is selected. This allows the sys-

tem designer to implement the Secure Learn feature or

use this fixed code word as part of a different key genera-

tion/tracking process or purely as a fixed code transmis-

sion.

3.4

SER_0, SER_1

(Encoder Serial Number)

SER_0 and SER_1 are the lower and upper words of

the device serial number, respectively. There are 32

bits allocated for the Serial Number and a selectable

configuration bit determines whether 32 or 28 bits will

be transmitted. The serial number is meant to be

unique for every transmitter.

WORD

ADDRESS

MNEMONIC

DESCRIPTION

KEY_0

64-bit crypt key

(word 0) LSb’s

KEY_1

64-bit crypt key

(word 1)

KEY_2

64-bit crypt key

(word 2)

KEY_3

64-bit crypt key

(word 3) MSb’s

SYNC_A

16-bit synch counter

SYNC_B/

SEED_2

16-bit synch counter B

or Seed value (word 2)

RESERVED

Set to 0000H

SEED_0

Seed Value

(word 0) LSb’s

SEED_1

Seed Value

(word 1) MSb’s

SER_0

Device Serial Number

(word 0) LSb’s

SER_1

Device Serial Number

(word 1) MSb’s

CONFIG

Configuration Word

Note:

Since SEED2 and SYNC_B share the

same memory location, Secure Learn and

Independent mode transmission (including

IR mode) are mutually exclusive.

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