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Controller Area Network

  • Artigo

Before joining Microsoft I worked for almost 8 years in the automotive industry developing various embedded devices.

One fascinating and not generally known aspect of automotive electronics is in-vehicle networks.

In-vehicle networks enable communication among distributed systems and at the same time provide a cost effective replacement of the wiring harness required to control every single device, sensor and actuator. They enable endless scenarios, since each device can adapt its behavior using information provided by other devices. As an example, at high speeds the radio can raise its volume and the roof can adjust to a more aerodynamic position. The front light beams can adapt their shape when the steering wheel is rotated to enter a curve.

Here’s an excellent illustration from Bosch that shows the integration of the devices very well-

Among the various networks adopted by the automotive industry, the Controller Area Network (CAN) is one of the most widely used.

CAN was originally developed by Bosch in the early 80’s, and became an international standard (ISO 11898) in the early 90’s. Now CAN is adopted by many other industries, such aircraft, train and maritime transportation, industrial automation and medical equipment.

CAN is a broadcast serial bus that operates at data rates of up to 1 Mbit/s. CAN is particularly robust to electromagnetic interference because it is a differential bus – i.e. it transmits complementary signals on two separate wires. The two wires are equally affected by electromagnetic interference, so the receiver node reads the difference between the two signals and rejects the noise. Additionally, wires are normally twisted so that noise is further reduced.

CAN is used to connect various types of Electronic Control Units (ECUs) across the vehicle. ECUs that have safety related functionalities (chassis ECUs) are usually on a separate CAN network from the ECUs that don’t (body electronics ECUs).

Chassis ECUs (shown in the picture above) control the power train and various safety related systems, such as braking, stability (ABS, ESP), steering, airbag and restrain systems. Chassis ECUs normally use high-speed CAN networks (e.g. 500 Kbit/s).

Body electronics ECUs are those controlling external and internal lighting units, dashboard display, dashboard and steering wheel buttons and levers, doors locks, power windows, power roof, entertainment systems (radio, navigation system and phone), seat controllers and parking aid systems. This category typically adopts lower speeds (e.g. 125 Kbit/s).

If you are interested in getting more information on CAN, here it is a quick reference:

  • Bosch - develops and manufactures automotive electronics systems.
  • CiA - CAN in Automation.
  • Kvaser - advanced CAN solutions.

- Luca

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