HCS410 datasheet(5/36 Pages) MICROCHIP

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HCS410

Preliminary

DS40158C-page 5

1.3

KEELOQ IFF

The HCS410 can be used as an IFF transponder for

veriﬁcation of a token. In IFF mode the HCS410 is ide-

ally suited for authentication of a key before disarming

a vehicle immobilizer. Once the key has been inserted

in the car’s ignition the decoder would inductively poll

the key validating it before disarming the immobilizer.

IFF validation of the token involves a random challenge

being sent by a decoder to a token. The token then gen-

erates a response to the challenge and sends this

response to the decoder (Figure 1-2). The decoder cal-

culates an expected response using the same chal-

lenge. The expected response is compared to the

response received from the token. If the responses

match, the token is identiﬁed as a valid token and the

decoder can take appropriate action.

The HCS410 can do either 16 or 32-bit IFF. The

HCS410 has two encryption algorithms that can be

used to generate a response to a challenge. In addition

there are up to two encoder keys that can be used by

the HCS410. Typically each HCS410 will be pro-

grammed with a unique encoder key(s).

In IFF mode, the HCS410 will wait for a command from

the base station and respond to the command. The

command can either request a read/write from user

EEPROM or an IFF challenge response. A given 16 or

32-bit challenge will produce a unique 16/32-bit

response, based on the IFF key and IFF algorithm

used.

FIGURE 1-2:

IBASIC OPERATION OF AN IFF TOKEN

IFF Key

Serial Number

KEELOQ

IFF

Algorithm

Serial Number

EEPROM Array

Challenge Received from Decoder

Response

Read by Decoder

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