MikroElektronika PIC Microcontrollers PIC18 Manuel d'utilisateur télécharger pdf (Page 2)

As shown in Figure 9.1, in a typical vehicle application there is usually more than one

CAN bus, and they operate at different speeds. Slower devices, such as door control,

climate control, and driver information modules, can be connected to a slow speed bus.

Devices that require faster response, such as the ABS antilock braking system, the

transmission control module, and the electronic throttle module, are connected to a

faster CAN bus.

The automotive industry’s use of CAN has caused mass production of CAN controllers.

Current estimate is that 400 million CAN modules are sold every year, and CAN

controllers are integrated on many microcontrollers, including PIC microcontrollers,

and are available at low cost.

Figure 9.2 shows a CAN bus with three nodes. The CAN protocol is based on CSMA/

CDþAMP (Carrier-Sense Multiple Access/Collision Detection with Arbitration on

Message Priority) protocol, which is similar to the protocol used in Ethernet LAN.

When Ethernet detects a collision, the sending nodes simply stop transmitting and wait

Air

conditioner

Door

switch

Instrument

panel

500Kb/s

Satellite

navigation

DVD

Radio

5Mb/s

Engine

Oil

pressure

Brakes

Gateway

125Kb/s

Head

lamps

Steering

Engine

temperature

Tire

pressure

Figure 9.1: Typical CAN bus application in a vehicle

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MikroElektronika PIC Microcontrollers PIC18 Manuel d'utilisateur Page 2