Introduction

Controller Area Network (CAN Bus)

Introduction
The CAN bus is a serial communications bus in which all connected control units can send as well as receive information. Data over the CAN operates at a rate of up to 500 K/bps (kilobits per second).

The CAN protocol was originally developed by Intel(TM) and Bosch in 1988 for use in the automotive industry to provide a standardized, reliable and cost-effective communications bus for a cars electronics to combat the increasing size of wiring harnesses.

The CAN bus was originally introduced on BMW automobiles in the 1993 740i/iL as a data link between the DME and AGS control units.







Data transmitted from any subscriber on a CAN bus does not contain addresses of the transmitting or receiving control unit. Instead, the content of the message (RPM, TD, Temp, etc) is labeled by an identifier code that is unique throughout the CAN. All of the subscribers receive the message and each one checks the message to see if it is relevant to that particular control unit.

If the message is relevant then it will be processed, if not, it will be ignored. The identifier code also determines the priority of the message. In a case where two control units attempt to send a message over a free bus line, the message with the higher priority will be transmitted first. The protocol of the CAN ensures that no message is lost, but stored by the sender and then re-transmitted later when it is possible.