What is optical network terminal
Controller Area Network or CAN protocol is a method of communication between various electronic devices like engine management systems, active suspension, ABS, gear control, lighting control, air conditioning, airbags, central locking etc embedded in an automobile. An idea initiated by Robert Bosch GmbH in 1983 to improve the quality of automobiles thereby making them more reliable, safe and fuel efficient. With the developments taking place in the electronics and semiconductor industry the mechanical systems in an automobile were being replaced by more robust electronics system which had an improved performance. New technologies, products and inventions with added or improved functions started to shape a complete new era for the automobile industry which promised more robust vehicles with use of electronics. The increasing number of electronic devices used communication signals with more complex interrelations between them. Thereby making the life difficult for automobile engineers when they designed systems wherein one electronic device needs to communicate with others to operate. Realizing the problem of communication between different electronic modules Robert Bosch came up with this new protocol called CAN which was first released in 1986. CAN provide a mechanism which is incorporated in the hardware and the software by which different electronic modules can communicate with each other using a common cable.
Need for CAN
A vehicle contains a network of electronic devices to share information/data with each other. For example A spark ignition engine requires a spark to initiate the combustion chamber at the correct time so it communicates with engine control unit that adjusts the exact timing for ignition to provide better power and fuel efficiency. Another example is of a transmission control unit that changes the ratio of gear automatically with the changing
speed. It uses information from engine control unit and various sensors in the system. Every electronic device has an ECU/MCU (electronic/microcontroller control unit) with its own set of rules to share/transfer information. For two or more devices to interact they should have the necessary hardware and software which allows them to communicate with each other. Before CAN was introduced in the automobiles, each electronic device was connected to other device using the wires (point to point wiring) which worked fine, when the functions in the system were limited. The figure below is the pictorial view of the point to point wiring connection.
One of the major problems for automotive engineers was linking the ECUs of the different devices so that real time information can be exchanged. CAN protocol was designed to address this problem. It laid down the rules through which the various electronic devices can exchange information with each other over a common serial bus. This in turn reduced the wiring connections to a great extend thereby reducing the bulkiness and complexity of the system. The image below shows how the different devices are connected using the CAN protocol.
Also the standard technology of time, asynchronous transmitter/receiver did not support multi domain communications. Domain is a group of electronic devices that have almost similar requirements to work in the system. For example CD/DVD PLAYER, GPS system, monitors and displays etc. form a single domain. Similarly air conditioning and climate control, dashboards, wipers, lights doors etc. form another domain. Hence the electronic devices implanted in a vehicle can be classified under different domain. CAN facilitates multi-domain communication for the engineers.
The table below shows the different domains