Road vehicles Controller area network (CAN) Part 4: Time-triggered communication
|Publication Date:||1 August 2004|
|ICS Code (Car informatics. On board computer systems):||43.040.15|
This part of ISO 11898 specifies time-triggered communication in the controller area network (CAN): a serial communication protocol that supports distributed real-time control and multiplexing for use within road vehicles. It is applicable to setting up a time-triggered interchange of digital information between electronic control units (ECU) of road vehicles equipped with CAN, and specifies the frame synchronisation entity that coordinates the operation of both logical link and media access controls in accordance with ISO 11898-1, to provide the time-triggered communication schedule.
NOTE Time-triggered CAN is a higher level protocol layer additional to the CAN protocol itself, which remains unchanged within the time-triggered communication. Time-triggered communication keeps the latency time of each message at a specified value independent of the CAN bus load. Time-triggered CAN is implemented on two levels: Level 1 is restricted to the cyclic message transfer, while Level 2, in addition, supports a global system time. Timetriggered CAN's cyclic, periodical communication is based on reference messages transmitted by a time master. Each period starting with a reference message is called a basic cycle and is subdivided into several time windows. The reference messages are used to synchronise and calibrate the time bases of all nodes to the time master's time base, providing a global time for the network. A mechanism is provided for alternative time masters to substitute for a failing time master.