2.
Kit Overview
This section describes the different blocks supported by the CARS.
Figure 2-1. CARS System Block Diagram
Main
Controller
Board
(SAMC21)
(ATA5702)
3D LF PEPS
and
3D LF
Transponder
LF Link
(125kHz)
LF Immobilizer Link
(125kHz)
Fob
Vehicle
SPI
UWB Verifier
(ATA8352)
SPI
UWB Prover
(ATA8352)
UWB Link
(6520 MHz)
UHF Link
(433.92 MHz)
RF Transmitter
RF Receiver
(ATA5831)
Immobilizer
Basestation and
LF Coil Driver
(ATA5291/3)
SPI
SPI
2.1
Immobilizer Block
The immobilizer is considered the system foundation because it must always work, even if the fob battery is dead,
and secures a vehicle against unauthorized engine starts. It consists of a base station, placed in the vehicle, that
provides the LF (125 kHz) magnetic field enabling a wireless link with the transponder in the fob to be established.
This LF immobilizer link is used to exchange the power supply and digital data between the vehicle and the passive
transponder.
The implemented immobilizer system supports Microchip’s OIP, which consists of an open/unlicensed protocol stack
based on AES-128 encryption. First, the
ReadUID
command is sent to the fob. The fob has to decode the
ReadUID
command and respond with its Unique ID (UID) value. If the received UID value is correct (matches the stored UID),
the start authentication command is issued and challenge data is sent to the fob based on the authentication type
(unilateral or bilateral). The fob receives the challenge, performs the encryption and sends a ciphered response back.
This response is received by the base station and verified to complete the authentication process.
Notes:
1.
The fob is a receive-only device; therefore, the ciphered response back to the base station is accomplished by
loading/unloading the magnetic field to encode the data.
2.
For more details on the OIP protocol, refer to the
ATAN0088 Open Source Immobilizer Protocol Stack
Application Note
(9195).
2.2
RKE Block
RKE functionality provides the means to lock or unlock and even start the vehicle from a long distance with a fob
carried by the user. The system consists of an RF receiver in the vehicle and an RF transmitter in the fob. Unlike the
immobilizer operation, the RKE operation requires a battery (CR2032 or equivalent) to be inserted in the fob.
ATAN0219
Kit Overview
©
2020-2022 Microchip Technology Inc.
and its subsidiaries
User Guide
DS50003051B-page 6
