7.4.1. Immobilizer

The system of an immobilizer consists of a passive priyemootvetchik (for a mutual identification), the key of the car mounted in a head, and the antenna Smartra block (Smart Transponder Antenna).

The Smartra block includes the built-in inductive aerial and the electronic schemes connected to the switch of ignition. The Smartra block is connected to the control unit the engine the special communication line.

Such way of management of the Smartra block is the most expedient since start of the engine the control unit operates the engine.

Fig. 7.77. Block diagram of the antenna block of an immobilizer

The control unit the engine makes an ignition key identification by means of the special coding algorithm operating in parallel in a priyemootvetchik. Start of the engine is possible only at coincidence of results of action of algorithm. In the control unit the engine stores data of all priyemootvetchik attached to the car.

The control unit by the engine and the Smartra block are reported among themselves on the special communication line. The control unit the engine establishes connection on the line K either with the Smartra block, or with other devices (for example, with the verifying device at maintenance) by turning on of the multiplexer and start of special procedures of communication. The multiplexer is a part of hardware of the control unit the engine. The Smartra block carries out communication through the priyemootvetchik which has been built in the ignition key. Communication is carried out on a radio frequency of 125 kHz. The Smartra block is established on the ignition switch near a frame send-receive radio antenna. The radio-frequency signal accepted by the frame aerial will be transformed by the Smartra block to messages for serial communication, and accepted from the control unit by the engine of the message will be transformed to the radio-frequency signal transferred through the aerial to a priyemootvetchik.

The Smartra block does not make an identification of a priyemootvetchik or calculation of algorithm of coding. It represents the advanced interface which will transform a data flow received on a radio frequency from a priyemootvetchik to sequence of the messages issued on the control unit by the engine, and on the contrary.

Priyemootvetchik – the Hitag2 type with advanced algorithm of coding. When programming key special data of the car which register its memory are entered into a priyemootvetchik. Record procedure – disposable therefore it is impossible to change contents of memory of a priyemootvetchik. Data are entered in the form of a chain into 9 bytes, made at manufacturer. Contents of memory of a priyemootvetchik share on two chains which carry the name "opoznavatel" and «the key password».

After that programming memory of a priyemootvetchik is blocked and its contents cannot be considered or changed. Priyemootvetchik passes from a condition "pure" "programmed" to a condition.

Besides, each priyemootvetchik has own identification number IDE in 32 bits. The numbers IDE of priyemootvetchik do not repeat. The number IDE is entered at manufacturer and can be read out only.

Opoznavatel and the password of a key are not transferred from the control unit by the engine to a priyemootvetchik or back. Results of action of algorithm of coding are transferred only. By result of coding to calculate special data of the car it is almost impossible.

For programming of keys or other purposes the control unit the engine incorporates to the verifying device as which the factory tester for the maintenance, used at service stations can serve. Communication is carried out according to the protocol of the line K of the control unit by the engine.