HCS410_01 Datasheet, PDF (4/36 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder and Transponder

HCS410
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
generates 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: BASIC OPERATION OF AN IFF TOKEN
Challenge Received from Decoder
EEPROM Array
IFF Key
Serial Number
KEELOQ
IFF
Algorithm
Read by Decoder
Serial Number Response
DS40158E-page 4
Preliminary
 2001 Microchip Technology Inc.