MODELS   all

The CAN data bus (Controller Area Network) is a data bus system specifically designed for used in vehicles. The CAN data bus is a bi-directional bus, that is, each connected control module is able to send and receive information. The CAN data bus consists of a special twisted two-core cable. The users (control modules) are connected to this cable. Transmission of data takes place redundantly via both cables, whereby the data bus levels are mirrored (that is, if the level on one cable is 0, the other cable transmits level 1 and vice versa). The twin-line concept is used for two reasons: for fault identification and as a safety concept. If a voltage peak occurs on just one line (e.g. due to EMC problems), the receivers can identify this as a fault and ignore the voltage peak.

If a short circuit or interruption occurs on one of the two CAN lines, a software-hardware linked safety concept allows switching to single-line operation. The defective data line is shut down. A specific data protocol controls how and when the participants can send and receive. The CAN data bus is significantly different to other data bus systems that are based on the participant addressing principle, in that it uses a message-related addressing system. That means, every CAN message is assigned a fixed address (identifier), which identifies the CAN message content (e.g. coolant temperature). The CAN protocol allows up to 2048 different CAN messages, whereby the addresses from 2033 to 2048 are permanently assigned. Data capacity per CAN message is 8 bytes.

A recipient only evaluates those CAN messages (data messages) which are stored in its list of CAN messages to be accepted (acceptance filtering). Data messages can only be sent when the CAN data bus is free (i.e. once a 3 bit interval has elapsed after the last data message, and no control module starts to send). The data bus level is then in recessive state (logical 1). If several control modules simultaneously start to send, a procedure initiates,

in which the highest priority CAN message is transmitted, without incurring a time or bit loss (arbitration). Every control module that loses the arbitration, automatically reverts to receiver and repeats its transmission attempt as soon as the CAN data bus becomes free. Besides data messages, there is also a request message used for calling a particular CAN message. The control module that can provide the requested data message then reacts to the request.