Vehicle bus

Key takeaways

Vehicle bus belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Vehicle bus to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Vehicle bus from memory before moving on to harder problems.

Reference excerpt

A vehicle bus is a specialized internal communications network that interconnects components inside a vehicle (e.g., automobile, bus, train, industrial or agricultural vehicle, ship, or aircraft). In electronics, a bus is simply a device that connects multiple electrical or electronic devices together. Special requirements for vehicle control such as assurance of message delivery, of non-conflicting messages, of minimum time of delivery, of low cost, and of EMF noise resilience, as well as redundant routing and other characteristics mandate the use of less common networking protocols. Protocols include Controller Area Network (CAN), Local Interconnect Network (LIN) and others. Conventional computer networking technologies (such as Ethernet and TCP/IP) are rarely used, except in aircraft, where implementations of the ARINC 664 such as the Avionics Full-Duplex Switched Ethernet are used. Aircraft that use Avionics Full-Duplex Switched Ethernet (AFDX) include the Boeing 787, the Airbus A400M and the Airbus A380. Trains commonly use Ethernet Consist Network (ECN). All cars sold in the United States since 1996 are required to have an On-Board Diagnostics connector, for access to the car's electronic controllers.

Background The main driving forces for the development of vehicle network technology have been the advances made in the electronics industry in general and government regulations imposed, especially in the United States, in order to make the automobiles environmentally friendly. With stringent emission standards for automobiles, it became impossible to attain the required degree of control without the help of on-board computing devices. On-board electronic devices have also contributed substantially to vehicle performance, occupant comfort, ease of manufacture and cost effectiveness. At one time, a car radio was likely the only electronic device in an automobile, but now almost every component of the vehicle has some electronic feature. Typical electronic modules on today's vehicles include the Engine Control Unit (ECU), the Transmission Control Unit (TCU), the Anti-lock Braking System (ABS) and body control modules (BCM). An electronic control module typically gets its input from sensors (speed, temperature, pressure, etc.) that it uses in its computation. Various actuators are used to enforce the actions determined by the module (turn the cooling fan on, change gear, etc.). The modules need to exchange data among themselves during the normal operation of the vehicle. For example, the engine needs to tell the transmission what the engine speed is, and the transmission needs to tell other modules when a gear shift occurs. This need to exchange data quickly and reliably led to the development of the vehicle network, as the medium of data exchange. The automotive industry quickly realized the complexity of wiring each module to every other module. Such a wiring design would not only be complex, it would have to be altered depending on which modules were included in the specific vehicle. For example, a car without the anti-lock brake module would have to be wired differently than one that included anti-lock brakes. The industry's answer to this problem was to create a central network in the vehicle. Modules could be 'plugged' into the network and would be able to communicate with any other module that was installed on the network. This design was easier to manufacture, easier to maintain and provided the flexibility to add and remove options without affecting the entire vehicle's wiring architecture. Each module, a node on the vehicle network, controls specific components related to its function and communicates with the other modules as necessary, using a standard protocol, over the vehicle network. Networks were not new, but their application to the vehicle was. The networks for the vehicles called for:

Low cost Immunity from external noise Ability to operate in harsh environments Overall robustness and reliability Although the vehicle network made modest demands on data throughput, the demand for more on-board computing is continuing to drive changes to these networks to provide higher-speed communication between modules. The control area network include the receiver and transmitter for the host to controller transmission and interlinking between the computers

Protocols, physical media and connectors There are several network types and protocols used in vehicles by various manufactures. Many companies are encouraging a standard communication protocol, but one has not been settled on.

Protocols Common vehicle buses protocols include:

A²B - (Automotive Audio Bus) An audio distribution protocol developed by Analog Devices[1] AFDX ARINC 429 Byteflight CAN – (Controller Area Network) an inexpensive low-speed serial bus for interconnecting automotive components D2B – (Domestic Digital Bus) a high-speed multimedia interface FlexRay – a general purpose high-speed protocol with safety-critical features IDB-1394 IEBus I²C ISO 9141-1/-2 J1708 and J1587 J1850 J1939 and ISO 11783 – an adaptation of CAN for commercial (J1939) and agricultural (ISO 11783) vehicles Keyword Protocol 2000 (KWP2000) – a protocol for automotive diagnostic devices (runs either on a serial line or over CAN) LIN – (Local Interconnect Network) a very low cost in-vehicle sub-network MOST – (Media Oriented Systems Transport) a high-speed multimedia interface Multifunction Vehicle Bus – part of the Train Communication Network IEC 61375. SMARTwireX SPI VAN – (Vehicle Area Network) UAVCAN – (Uncomplicated Application-level Vehicular Communication And Networking) mostly used in electric aircraft, drones, satellites, and robotics.

Physical transmission media Some examples of physical transmission media use in vehicle networks:

Single wire Twisted Pair Fibre optic IEEE 1394 MIL-STD-1553, developed for use in military avionics, it is now widely used in spacecraft too. Adopted for the MiG-35. MIL-STD-1773, roughly MIL-STD-1553 with optic cabling Power-line communication [2]

Connectors OBD-2 (16 pin) Additionally, many major car manufacturers use their own proprietary vehicle bus standards, or overlay proprietary messages over open protocols such as CAN.

J1939 (9 pin) Commercial class vehicles have Type-I or Type-II connectors that support CAN based communication per the SAE J1939 protocol.[3]

Protocols usage

References

External links Automotive buses

Worked examples

Example 1 — a first encounter with Vehicle bus

Start with the simplest possible case. Write down what Vehicle bus claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Vehicle bus before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Vehicle bus ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Vehicle bus

In research: Vehicle bus appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Vehicle bus in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Vehicle bus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer buses, so understanding it makes those chapters shorter.
In everyday life: Look for Vehicle bus outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Vehicle bus in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Vehicle bus means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Vehicle bus out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Vehicle bus in simple terms?

A vehicle bus is a specialized internal communications network that interconnects components inside a vehicle (e.g., automobile, bus, train, industrial or agricultural vehicle, ship, or aircraft). In electronics, a bus is simply a device that connects multiple electrical or electronic devices toget…

Why does Vehicle bus matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Vehicle bus?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Vehicle bus.