CAN Bus Guide

CAN Bus Guide – Message Priority

A Comprehensible Guide to Controller Area Network (CAN Bus) by Wilfried Voss
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Per definition, CAN nodes are not concerned with information about the system configuration (e.g. node address, etc.), hence CAN does not support node IDs. Instead, receivers process messages by means of an acceptance filtering process, which decides whether the received message is relevant for node’s application layer or not. There is no need for the receiver to know the transmitter of the information and vice versa.

CAN data transmissions are distinguished by a unique message identifier (11/29 bit), which also represents the message priority. A low message ID represents a high priority. A single CAN node may send or receive any number of messages, which contributes, yet again, to a maximum level of flexibility.

High priority messages will gain bus access within shortest time even when the bus load is high due to the number of lower priority messages.

Message transmissions are usually event-driven to reduce the bus load and that guarantees short latency times for real-time applications.