HCS300-SLASHP datasheet(6/28 Pages) MICROCHIP

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HCS300

DS21137F-page 6

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

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 (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.

3.3

Reserved

Must be initialized to 0000H.

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. Although there

are 32 bits allocated for the serial number, only the

lower order 28 bits are transmitted. The serial number

is meant to be unique for every transmitter.

3.5

SEED_0, SEED_1 (Seed Word)

The 2-word (32-bit) seed code will be transmitted when

all three buttons are pressed at the same time (see

Figure 4-2). This allows the system designer to imple-

ment the secure learn feature or use this fixed code

word as part of a different key generation/tracking pro-

cess.

3.5.1

AUTO-SHUTOFF TIMER ENABLE

The Most Significant bit of the serial number (Bit 31) is

used to turn the Auto-shutoff timer on or off. This timer

prevents the transmitter from draining the battery

should a button get stuck in the on position for a long

period of time. The time period is approximately

25 seconds, after which the device will go to the Time-

out mode. When in the Time-out mode, the device will

stop transmitting, although since some circuits within

the device are still active, the current draw within the

Shutoff mode will be higher than Standby mode. If the

Most Significant bit in the serial number is a one, then

the Auto-shutoff timer is enabled, and a zero in the

Most Significant bit will disable the timer. The length of

the timer is not selectable.

WORD

ADDRESS

MNEMONIC

DESCRIPTION

KEY_0

64-bit encryption key

(word 0) LSb’s

KEY_1

64-bit encryption key

(word 1)

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

SEED_0

Seed Value (word 0)

SEED_1

Seed Value (word 1)

RESERVED

Set to 0000H

CONFIG

Config Word

Note:

The MSB of the serial number contains a bit

used to select the Auto-shutoff timer.

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