Time Triggered CAN (TTCAN) 2001-01-0073

Connecting microcontrollers, sensors and actuators by several communication systems is state of the art within the electronic architectures of modern vehicles. The communication among these components is widely based on the event triggered communication on the Controller-Area-Network (CAN) protocol. The arbitrating mechanism of this protocol ensures that all messages are transferred according to the priority of their identifiers and that the message with the highest priority will not be disturbed. In the future some mission critical subnetworks within the upcoming generations of vehicle systems, e.g. x-by-wire systems (xbws), will additionally require deterministic behavior in communication during service. Even at maximum bus load, the transmission of all safety related messages must be guaranteed. Moreover it must be possible to determine the point of time when the message will be transmitted with high precision.

One way to solve this issue using CAN is the extension of the standard CAN protocol to a time triggered protocol TTCAN. The communication is based on the periodic transmission of a reference message by a time master. This allows to introduce a system wide global network time with high precision. Based on this time the different messages are assigned to time windows within a basic cycle. A big advantage of TTCAN compared to classic scheduled systems is the possibility to transmit event triggered messages in certain “arbitrating” time windows as well.