HCS362-I datasheet(2/38 Pages) MICROCHIP

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HCS362

DS40189D-page 2

Preliminary

GENERAL DESCRIPTION

The HCS362 is a code hopping encoder designed for

secure Remote Keyless Entry (RKE) systems. The

HCS362 utilizes the KEELOQ® code hopping technol-

ogy, which incorporates high security, a small package

outline and low cost, to make this device a perfect

solution for unidirectional remote keyless entry sys-

tems and access control systems.

The HCS362 combines a 32-bit hopping code

generated by a nonlinear encryption algorithm, with a

28/32-bit serial number and 9/5 status bits to create a

69-bit transmission stream. The length of the transmis-

sion eliminates the threat of code scanning. The code

hopping mechanism makes each transmission unique,

thus rendering code capture and resend (code grab-

bing) schemes useless.

The crypt key, serial number and configuration data are

stored in an EEPROM array which is not accessible via

any external connection. The EEPROM data is pro-

grammable but read protected. The data can be veri-

fied only after an automatic erase and programming

operation. This protects against attempts to gain

access to keys or manipulate synchronization values.

The HCS362 provides an easy to use serial interface

for programming the necessary keys, system parame-

ters and configuration data.

1.0

SYSTEM OVERVIEW

Key Terms

The following is a list of key terms used throughout this

data sheet. For additional information on KEELOQ and

Code Hopping, refer to Technical Brief 3 (TB003).

• RKE - Remote Keyless Entry

• Button Status - Indicates what button input(s)

activated the transmission. Encompasses the 4

button status bits S3, S2, S1 and S0 (Figure 3-2).

• Code Hopping - A method by which a code,

viewed externally to the system, appears to

change unpredictably each time it is transmitted.

• Code word - A block of data that is repeatedly

transmitted upon button activation (Figure 3-2).

• Transmission - A data stream consisting of

repeating code words (Figure 7-1).

• Crypt key - A unique and secret 64-bit number

used to encrypt and decrypt data. In a symmetri-

cal block cipher such as the KEELOQ algorithm,

the encryption and decryption keys are equal and

will therefore be referred to generally as the crypt

key.

• Encoder - A device that generates and encodes

data.

• Encryption Algorithm - A recipe whereby data is

scrambled using a crypt key. The data can only be

interpreted by the respective decryption algorithm

using the same crypt key.

• Decoder - A device that decodes data received

from an encoder.

• Decryption algorithm - A recipe whereby data

scrambled by an encryption algorithm can be

unscrambled using the same crypt key.

• Learn – Learning involves the receiver calculating

the transmitter’s appropriate crypt key, decrypting

the received hopping code and storing the serial

number, synchronization counter value and crypt

key in EEPROM. The KEELOQ product family facil-

itates several learning strategies to be imple-

mented on the decoder. The following are

examples of what can be done.

- Simple Learning

The receiver uses a fixed crypt key, common

to all components of all systems by the same

manufacturer, to decrypt the received code

word’s encrypted portion.

- Normal Learning

The receiver uses information transmitted

during normal operation to derive the crypt

key and decrypt the received code word’s

encrypted portion.

- Secure Learn

The transmitter is activated through a special

button combination to transmit a stored 60-bit

seed value used to generate the transmitter’s

crypt key. The receiver uses this seed value

to derive the same crypt key and decrypt the

received code word’s encrypted portion.

• Manufacturer’s code – A unique and secret 64-

bit number used to generate unique encoder crypt

keys. Each encoder is programmed with a crypt

key that is a function of the manufacturer’s code.

Each decoder is programmed with the manufac-

turer code itself.

The HCS362 code hopping encoder is designed specif-

ically for keyless entry systems; primarily vehicles and

home garage door openers. The encoder portion of a

keyless entry system is integrated into a transmitter,

carried by the user and operated to gain access to a

vehicle or restricted area. The HCS362 is meant to be

a cost-effective yet secure solution to such systems,

requiring very few external components (Figure 2-1).

Most low-end keyless entry transmitters are given a

fixed identification code that is transmitted every time a

button is pushed. The number of unique identification

codes in a low-end system is usually a relatively small

number. These shortcomings provide an opportunity

for a sophisticated thief to create a device that ‘grabs’

a transmission and retransmits it later, or a device that

quickly ‘scans’ all possible identification codes until the

correct one is found.

The HCS362, on the other hand, employs the KEELOQ

code hopping technology coupled with a transmission

length of 66 bits to virtually eliminate the use of code

‘grabbing’ or code ‘scanning’. The high security level of

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