Have you ever wondered how many sensors are there in a car and how are they connected with each other to perform efficiently?

Yes, there are hundreds of sensors in today’s highly advanced and electronically controlled cars. Before 1983 it was a cumbersome/hectic task to install many numbers of sensors in the car because to connect each sensor there required a separate wire to connect it with the dashboard/ECU of the vehicle (point to point connection). This results in a huge bundle of wires installed in the car and that number of wires was also a challenge to handle. Also, the automobile engineers were restricted to use only a certain number of sensors in the car. 

So, to overcome this problem, in 1983 Robert Bosch came with a highly advanced and a very simple solution i.e., CAN PROTOCOL, but was officially released in 1986.

CAN PROTOCOL is a two message, two wired based communication protocol. CAN stands for Controlled Area Network. This protocol is a set of instructions which facilitate the sensors and ECU of the vehicle to communicate with each other like ABS system, Braking system, Fuel meter, Smart Air conditioning, seat belt sensor, Airbag safety and many more.

This protocol defines how the data/information will be shared between various sensors and ECU in the car with minimum no. of wires i.e., only 2 which is called CAN Bus. It does not follow master-slave communication which means this protocol does not need a host computer so any node can act as a master. Here each periphery connected to the CAN Bus is known as a node.

 Connections between various sensors without CAN protocol (fig:1)

Here in fig:1, we can clearly see that how various nodes are connected to ECU with separate wire making its a huge bunch of wire.



Connections between various node with CAN protocol(fig:2)

Here in fig:2, we can see that all the nodes are connected to each other through CAN protocol where only two wires are used one being CAN High Bus for transmission of data at high speed of up to 1mbps and another being CAN Low Bus for transmission of data at low speed of up to 125kbps.

With not being of master-slave type communication each node can read or write a message on the CAN bus, the node checks the availability of the bus and writes a CAN Frame on the bus. Here frame refers to a structure which contains a meaningful sequence of bits or bytes of the transferred data. 

As mentioned, CAN is a two-message based protocol and each message have its own identifier which acts as the unique identity of the message, a can message contains up to 10 bytes of data, protocols are basically of two types one is address based in which each data consist of the address of its destination and the second one being message-based which consist of identifier as the unique id of the message. Node requiring the message of a particular identifier can read the message from the can bus by intercepting the proper identifier.

Here CAN has two types of identifier, one being 11 bit and another one being 29-bit identifier which is also known as an extended identifier. CAN device comes in two categories:

CAN2.0A are the devices which have an 11-bit identifier.

CAN2.0B is the devices which have a 29-bit identifier.

CAN Messages Frames:  There are four types of message frames in CAN protocol:

  1. Data Frame

  2. Remote Frame

  3. Error Frame

  4. Overload Frame


                      Further discussion on frames will be in the second part.





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