Controller Area Network for Can

 

Introduction to CAN ( Controller Area Network)

 

CAN BUS is set to become the new standard for data interchange between electronic components in cars. It is an ISO approved standard and is a low cost real time communication protocol.

Although developed by Robert Bosch in 1984, CAN wasn’t used in production vehicles until it made an appearance in 1992 on high end Mercedes cars. Nowadays with the price and availability of silicon a lot better than the 80’s and 90’s, CANBUS is making an appearance on almost all new cars.

Initially CAN BUS was only ever used for the engine management side of things. In the early Mercedes car CanBus was used to connect the Power Systems electronic control units. Now the technology has matured, and knowledge is more wide spread of the possibilities of CAN BUS, it is also being used to link together Body Control Modules. These body control modules are usually connected via a second, slower CANBUS. This allows the main high-speed CAN BUS to concentrate on high importance data around such as Anti-Lock Braking System data.

The high speed CanBus networks generally run at 500k bits/sec, where as the slower Body Control Can will run at 125k bits/sec.

 

Techie Stuff…

 

CAN is a serial bus system with Multimaster capabilities. This means that many nodes can transmit and receive data at the same time. When a node is transmitting it’s message, it is put on the BUS. All the nodes then receive the message. Depending on the receiving nodes address, the message is either discarded because it is not meant for that node, or it is accepted and processed. A message can also be given a priority. A message of high priority will obviously take precedence of using the canbus over a lower priority.

One of the outstanding features of Can is the reliability and error detection. The Can controller will register a nodes error and evaluates it to provide necessary errors. One problem with this however is that if one node fails, the whole network can fail. This is another reason for putting Power System and Body Control Modules on a separate network. If your electric window control module fails you still want your car to start!