HCS412SN datasheet(2/44 Pages) MICROCHIP

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HCS412

DS41099C-page 2

Preliminary

GENERAL DESCRIPTION

The HCS412 combines patented KEELOQ code hop-

ping technology with bi-directional transponder chal-

lenge-and-response security into a single chip solution

for logical and physical access control.

When used as a code hopping encoder, the HCS412 is

ideally suited to keyless entry systems; vehicle and

garage door access in particular. The same HCS412

can also be used as a secure bi-directional transponder

for contactless token verification. These capabilities

make the HCS412 ideal for combined secure access

control and identification applications, dramatically

reducing the cost of hybrid transmitter/transponder

solutions.

1.0

SYSTEM OVERVIEW

Key Terms

The following is a list of key terms used throughout this

data sheet. For additional information on terminology,

please refer to the KEELOQ introductory Technical Brief

(TB003).

• RKE - Remote Keyless Entry.

• PKE - Passive Keyless Entry.

• Button Status - Indicates what transponder but-

ton input(s) activated the transmission. Encom-

passes the 4 button status bits LC0, 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

(Section 1.1.3).

• Code word - A block of data that is repeatedly

transmitted upon button activation (Section 3.2).

• Transmission - A data stream consisting of

repeating code words.

• 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.

• Transponder Reader (Reader, for short) - A

device that authenticates a token using bi-direc-

tional communication.

• 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 (Section 6.1). The KEELOQ prod-

uct family facilitates several learning strategies to

be implemented 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.

• Anticollision - A scheme whereby transponders

in the same field can be addressed individually

preventing simultaneous response to a command

(Section 4.3.1).

• IFF - Identify Friend or Foe (Section 1.2).

• Proximity Activation - A method whereby an

encoder automatically initiates a transmission in

response to detecting an inductive field

(Section 4.4.1).

• Transport code - An access code, ‘password’

known only by the manufacturer, allowing pro-

gram access to certain secure device memory

areas (Section 4.3.3).

• AGC - Automatic Gain Control.

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