Automotive[ edit ] The modern automobile may have as many as 70 electronic control units ECU for various subsystems. Some of these form independent subsystems, but communications among others are essential. A subsystem may need to control actuators or receive feedback from sensors. The CAN standard was devised to fill this need.
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Automotive[ edit ] The modern automobile may have as many as 70 electronic control units ECU for various subsystems. Some of these form independent subsystems, but communications among others are essential. A subsystem may need to control actuators or receive feedback from sensors. The CAN standard was devised to fill this need. One key advantage is that interconnection between different vehicle systems can allow a wide range of safety, economy and convenience features to be implemented using software alone - functionality which would add cost and complexity if such features were "hard wired" using traditional automotive electrics.
Similarly, inputs from seat belt sensors part of the airbag controls are fed from the CAN bus to determine if the seat belts are fastened, so that the parking brake will automatically release upon moving off.
Parking assist systems: when the driver engages reverse gear, the transmission control unit can send a signal via the CAN bus to activate both the parking sensor system and the door control module for the passenger side door mirror to tilt downward to show the position of the curb. The CAN bus also takes inputs from the rain sensor to trigger the rear windscreen wiper when reversing.
Auto brake wiping: Input is taken from the rain sensor used primarily for the automatic windscreen wipers via the CAN bus to the ABS module to initiate an imperceptible application of the brakes whilst driving to clear moisture from the brake rotors. Some high performance Audi and BMW models incorporate this feature. Sensors can be placed at the most suitable place, and their data used by several ECUs.
For example, outdoor temperature sensors traditionally placed in the front can be placed in the outside mirrors, avoiding heating by the engine, and data used by the engine, the climate control, and the driver display. In recent years, the LIN bus standard has been introduced to complement CAN for non-critical subsystems such as air-conditioning and infotainment, where data transmission speed and reliability are less critical.
Other[ edit ] The CAN bus protocol has been used on the Shimano DI2 electronic gear shift system for road bicycles since , and is also used by the Ansmann and BionX systems in their direct drive motor.
The CAN bus is also used as a fieldbus in general automation environments, primarily due to the low cost of some CAN controllers and processors. The CueScript teleprompter range uses CAN bus protocol over coaxial cable, to connect its CSSC — Desktop Scroll Control to the main unit The CAN bus protocol is widely implemented due to its fault tolerance in electrically noisy environments such as model railroad sensor feedback systems by major commercial Digital Command Control system manufacturers and various open source digital model railroad control projects.
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Automotive electronics is a major application domain. Two or more nodes are required on the CAN network to communicate. A node may interfaces to devices from simple digital logic e. Such a computer may also be a gateway allowing a general purpose computer like a laptop to communicate over a USB or Ethernet port to the devices on a CAN network. All nodes are connected to each other through a physically conventional two wire bus. This bus uses differential wired-AND signals. A 0 data bit encodes a dominant state, while a 1 data bit encodes a recessive state, supporting a wired-AND convention, which gives nodes with lower ID numbers priority on the bus.
Receivers consider any differential voltage of less than 0. ISO ISO , also called low-speed or fault-tolerant CAN up to Kbps , uses a linear bus, star bus or multiple star buses connected by a linear bus and is terminated at each node by a fraction of the overall termination resistance. Electrical properties[ edit ] With both high-speed and low-speed CAN, the speed of the transition is faster when a recessive to dominant transition occurs since the CAN wires are being actively driven.
The speed of the dominant to recessive transition depends primarily on the length of the CAN network and the capacitance of the wire used. High-speed CAN is usually used in automotive and industrial applications where the bus runs from one end of the environment to the other.
Fault-tolerant CAN is often used where groups of nodes need to be connected together. The specifications require the bus be kept within a minimum and maximum common mode bus voltage, but do not define how to keep the bus within this range. The CAN bus must be terminated. The termination resistors are needed to suppress reflections as well as return the bus to its recessive or idle state.
Low-speed CAN uses resistors at each node. Other types of terminations may be used such as the Terminating Bias Circuit defined in ISO  A terminating bias circuit provides power and ground in addition to the CAN signaling on a four-wire cable. This provides automatic electrical bias and termination at each end of each bus segment.
CAN FD ISO 11898-1