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How CAN (Controlled Area Network) networks function?

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As per an article published in Elektronik Praxis, in a line structure, Controlled Area Networks are typically arranged where 120 Ohm terminating resistors are placed at each end of the line. Permission of Stubs is in a limited extension and in automotive applications, a star-type bus is possible. In each network, the number of participants is not limited by protocol but component performance is also a major depending on factor.

If CAN networks are needed to be extended then CAN repeaters are for multiple uses. A physical coupling of two or more segments of a CAN bus system can be established that can be implemented in tree or star topologies or available to add long drop lines. Network segments, in addition, can be electrically decoupled by using a galvanic isolated repeater.

The CAN bus communication is done via “telegrams” that contain both “control bits” and “data bits”. The frame is considered to be one of the standard configurations for such a telegram.

  • Data Frame is mainly used for data transmission for one or more receivers from a transmitter at the initiative of the transmitter.
  • Remote Frame can be used for a bus subscriber where they can request for sending a certain message from a data source. 
  • Error Frame is for all bus subscribers where the transmitter or receiver can signalize a detected error in the transmission line. 
  • Overload Frame where the CAN controller can notify its overload; but it’s no longer implemented as the controller’s performance is sufficient to handle any such overload. 

The content of the CAN message has been denoted by the (message) identifier and not by the device.

In a measurement system, temperature, voltage, and pressure have been assigned with a separate identifier. Under a single identifier, several parameters can be united until and unless the maximum length of the data field is not exceeded.

On the identifier basis, the receiving devices decided whether a message is relevant to them or not, and the message stream can be filtered out available on the bus.

The CAN identifier got a standard format of usually 11 bits; where 2,048 different messages per system can be distinguished and are also sufficient for a number of applications.

However, 29-bit identifiers are mostly used to make the definition possible for up to 512 million different messages for special applications such as Trucks.



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