Annexures

CAN OVERVIEW

CAN stands for "Controller Area Network" and is defined in the ISO 11898 specification.

CAN BUS COMPONENTS

CAN Controller receives the transfer data from the microcomputer integrated into the control unit/device (also known as CAN Node). The CAN controller processes this data and relays it to the CAN transceiver. Also, the CAN controller receives data from the CAN transceiver, processes it, and relays it to the microcomputer integrated into the control unit/device (CAN Node).

CAN Transceiver is a transmitter and receiver in one. It converts the CAN controller's data into electrical signals and sends this data over the data bus lines. Also, it receives data and converts this data for the CAN controller.

CAN Data Bus Termination is a resistor (R) typically 120 ohms. It prevents data sent from being reflected at the ends and returning as an echo and ensures that the bus gets the correct DC levels.

MAXIMUM BUS SPEED & CABLE LENGTH

The CAN bus uses inexpensive twisted-pair wires to send data. All the nodes are connected to the same line (bus) with small branch lines. The signals on the two CAN lines have the same data sequence, but their amplitudes are opposite. So, if a pulse on the CAN-H line goes from 2.5V to 3.75V, then the corresponding pulse on the CAN-L line goes from 2.5V to 1.25V (opposite to CAN-H).

According to the standard, the maximum speed of a CAN bus is 1 Mbit/second. At a speed of 1 Mbit/s, a maximum cable length of about 40 meters (130 ft.) can be used. This is because the arbitration scheme requires that the wavefront of the signal can propagate to the most remote node and back again before the bit is sampled.

• The maximum speed achievable is 1Mbps.

• The maximum length achievable is 500 meters at a lower speed of 125 Kbps.

• The bus should be terminated at both ends with 120-ohm resistance.

Removal of one node will not affect the communication in the bus.