Radio frequency locking (RFL) system description

Remote control key

The remote control key contains the following function elements:

 RF transmitter stage

 Recognition of key position

 Coding stage

 EEPROM as non-volatile data memory for data retention while changing batteries

 LED for indication of battery status

 2 lithium button cells as power supply

Control module

The control module contains the following function elements:

 RF receiver

 Interface for central locking and anti-theft alarm system

 Interface to engine electronic module (immobilizer function)

 Immobilizer indicator light control

 Input c. 15

 Input for door contact check

 Coding stage

 EEPROM as non-volatile data memory for data retention in the event of a power failure or while changing batteries

Communication between remote control key and receiver (control module)

The telegrams from the remote control key are transmitted coded.In the control module, the telegram is decoded and compared with a stored value.

A telegram is accepted as valid by the control module when the telegram from the remote control key is "synchronous" with the value calculated by the control module.

The telegram coding is changed each time the remote control key is actuated. In this manner, telegrams already transmitted become invalid making it impossible to monitor the radio frequency telegram.

Resynchronization

If a key is actuated more than 255 times in sequence outside of the range of the receiver (control module), the radio frequency telegram is desynchronized.

In such cases, the receiver (control module) can be resynchronized to the remote control key telegram by actuating the key (opening and closing) twice within 7 s.

Note

Resynchronization is only possible for remote control keys which have not been disabled.