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Today's vehicles contain hundreds of circuits, sensors, and many other electrical components. Communication is needed among the many circuits and functions of the vehicle. For example, when the driver presses the headlights switch on the dashboard, the headlights react. For this to occur, communication is needed between the dashboard switch and the front of the vehicle. In current vehicle systems this type of communication is handled via a dedicated wire through point-to-point connections. If all possible combinations of switches, sensors, motors, and other electrical devices in fully featured vehicles are accumulated, the resulting number of connections and dedicated wiring is enormous. Networking provides a more efficient method for today's complex in-vehicle communications.

In-vehicle networking, also known as multiplexing, is a method for transferring data among distributed electronic modules via a serial data bus. Without serial networking, inter-module communication requires dedicated, point-to-point wiring resulting in bulky, expensive, complex, and difficult to install wiring harnesses. Applying a serial data bus reduces the number of wires by combining the signals on a single wire through time division multiplexing. Information is sent to individual control modules that control each function, such as anti-lock braking, turn ignals, and dashboard displays (see figure 1).

As the electrical content of today's vehicles continues to increase the need for networking is even more evident. For example, some high-end luxury cars contain more than three miles and nearly 200 pounds of wiring. The resulting number of connectors creates a reliability nightmare.

BENEFITS OF NETWORKING

In-vehicle networking provides many system-level benefits, many of which are only beginning to be realized.
" A decreased number of dedicated wires is required for each function, and thus reduces the size of the wiring harness. System cost, weight, reliability, serviceability, and installation are improved.
" Common sensor data, such as vehicle speed, engine temperature, etc. are available on the network, so data can be shared, thus eliminating the need for redundant sensors.
" Networking allows greater vehicle content flexibility because functions can be added through software changes. Existing systems require an additional module or additional I/O pins for each function added.
" Car manufacturers are discovering new features that are enabled by networking. For example, the 1996 Lincoln Continental's Memory Profile System stores each driver's preference for ride firmness, seat positions, steering assist effort, mirror positions, and even radio station presets.

However, for networking to expand into higher volume economy class vehicles, the overall system benefits need to outweigh the costs. Standardized protocols will enable this expansion. Automotive manufacturers and various automotive industry standards organizations have been working for many years to develop standards for in-vehicle networking. Many standards such as VAN, ABUS, CAN, and SAE J1850 have been developed, but SAE J1850 and CAN 2.0 (Controller Area Network) are the predominant standards.

The early days of networking involved proprietary serial buses using generic UART (Universal Asynchronous Receiver/Transmitter) or custom devices. This was acceptable in the US because the Big Three (Ford, GM, Chrysler) were vertically integrated and were not highly dependent on external suppliers.

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