Bosch CAN bus

A controller area network (CAN) employs a single line, or bus, to convey data to all components that make up the network. Individual components—computers, sensors, display panels, stepper motors, and other devices—respond only to those signals addressed to them. These components, or stations, still need power lines, but one signal line suffices for all. Multiplexing is not too different than old-fashioned telephone systems that rang every phone on the line. By counting the number of rings, you knew who should pick up the receiver.

To make production changes easier, message content, rather than the name of the intended receiving station, functions as the address. This enables new stations to be added without modifying the transmitters. An 11- or 29-bit word prefaced to each data packet identifies message content. Thus, engine-speed data will be received by all stations, but will be of interest only to the computer and the operator display panel.

Upon acceptance of a message, the receiving station scans it for errors and acknowledges receipt. Transmission speed ranges between 125 kb (1 kb = 1000 bits/ second) and 1Mb. Messages whose content changes frequently, such as the voltage drop that signals injector opening, have priority over routine traffic.

The CAN protocol has fairly wide use for automotive and truck applications, and will, experts say, become universal within the next decade.

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