The following functions are grouped in the Car Access System (CAS):
The CAS consists of the CAS control unit and the electronic ignition/starting switch with key recess and START/STOP button.
Access to the vehicle is achieved by proof of authorisation. The proof is provided by the following items belonging to the vehicle
Emergency access: Emergency access to the vehicle, e.g. in the case of a discharged battery, is possible using the mechanical key tooth.
The CAS is used to handle the following functions via communication with the transponder in the key:
In the case of vehicle personalisation, when the remote control key (1 to 4) is recognised, the values are called up that were last set for this key (Key Memory) for the seat, mirror, air conditioner and radio functions.
Information is exchanged between the ”body” components via the K-CAN PERIPHERIE data bus. Communication with the vehicle environment takes place across the K-CAN SYSTEM data bus. Necessary signals are transferred bidirectionally between the two data buses using the ”Repeater” functionality.
The data exchange in the entire vehicle runs across the K-CAN SYSTEM data bus, e.g. between:
Via the K-CAN PERIPHERIE data bus, data exchange runs between:
The CAN repeater function in the CAS connects the physically separate data buses K-CAN SYSTEM and K-CAN PERIPHERIE into a logical ring. The function ensures implementation of the information required on the other data bus.
The CAS control unit has the ”master function” for the central locking system electronics, the power window electronics and the Car Access electronics.
Note: For diagnosis authentication, terminal control without ZAS is possible by means of CAS-internal functions.
Data of the car immobilisation system to release the ignition and injection system is transferred between CAS/ZAS and DME.
The switch-on and switch-off conditions for the interior lights are transferred by the central locking system and the CAS via the K-CAN PERIPHERIE data bus to the power module.
To display the state of the KiSi child safety lock, the red LED in the KiSi button in the switch block of the driver's door is activated by the CAS Car Access System. In the event of a fault, the CAS sends a signal to the Check Control for display in the instrument cluster.
The ring coil integrated in the ZAS is supplied with power by the CAS. The transponder communication and implementation of the write-read signals are handled in the CAS.
The CAS controls ”locking” and ”ejection” of the key depending on identification of ”valid” or ”not valid”. The CAS evaluates the function of the SST START/STOP button and passes the results to the K-CAN SYSTEM data bus.
If a crash signal is transferred by the airbag control unit via the CAS to the door modules when the doors are locked, the TM door modules are enabled with high priority for unlocking.
Flash download: The authentication procedure present in every control unit that is subject to the risk of manipulation and can be flash-programmed, which only permits re-programming when the corresponding authentication has been proven, is also implemented in the CAS.
Diagnosis authentication of the channel: In the CAS, authentication is implemented in the Security Authentication Module (SAM). The SAM checks and regulates the access data and access rights for the complete vehicle for a certain diagnosis channel, i.e. the authentication is checked first and then diagnosis is enabled for the rest of the vehicle in various stages.
Coding option for six functions of the central locking system.
In the case of automatic transmissions with electrical gearshifts, the Key Lock/Interlock function is not coded, as the parking lock (gear selector lever at ”P”) is set automatically when the key is removed.
The information arriving from the TM door modules across the K-CAN PERIPHERIE data bus is evaluated in the CAS. If a local anti-repeat circuit is active in a TM door module, the CAS sets a global anti-repeat circuit. This locks the central-locking function of the individual nodes.
The CBS data stored in the CAS can be queried per diagnosis command and also by telephone as follows:
The activated control unit sends its data to the CAS. From the CAS, the data is routed via telephone to the diagnosis.
So that vehicle-specific data is not lost when the instrument cluster is replaced, it is stored redundantly in the CAS.
As the vehicle is being assembled, the key data and other vehicle-specific data is entered in the CAS control unit at the factory. Here, the DME digital engine electronics and CAS control unit are synchronised.
These components are initialised at the factory within the system in the vehicle (key, FBD transmitter, DME).
Note: In the case of a spare part, the key and/or CAS itself is/are delivered preinitialised according to the individual 17-digit VIN.
Remote controls and/or spare keys can only be ordered from a central parts warehouse.
The key data for each vehicle identification number is stored in and can be called up from the database.
Using this data, a remote control can be programmed so that it matches the vehicle.
If a remote control is lost, it can be disabled via the diagnosis interface as follows:
Note: If the remote control is found again, it can be re-enabled in the same way.
To replace the CAS control unit, proceed as follows:
Following synchronisation, the vehicle is ready to drive once again.
After a DME has been replaced, in exactly the same way as for the CAS, the control units must be synchronised.