Put the Right Bus in Your Car The amazing array of features available in today’s cars has spawned new in-vehicle bus standards. by Karen Parnell tems, have spurred annual growth rates as bandwidth and speed restrictions make it Automotive Product Manager high as 16%, according to the Institute of difficult for these serial, event-driven buses Xilinx, Inc. Electrical and Electronics Engineers to handle newer real-time applications. [email protected] (IEEE). The IEEE forecasts that electron- A number of new bus standards have ics will account for 25% of the cost of a emerged featuring time-triggered protocols The next few years will be a rocky road for mid-size car by 2005. and optical data buses. These in-car bus net- automobile electronics designers. No sin- One high-growth area is telematics sys- works can be divided into four categories: gle in-car data bus can adequately handle tems – the convergence of mobile telecom- • Body control – dashboard/instrument the entertainment, safety, and intelligent- munications and information processing panel clusters, mirrors, seat belts, door control requirements of the cars that will in cars. Significantly, telematics applica- locks, and passive airbags roll off assembly lines in North America, tions exhibit market characteristics similar Europe, and Asia. to those of consumer products: short time • Entertainment and driver-information Choosing the right data bus can lead to to market, short time in market, and systems – radios, Web browsers, a competitive advantage, but the selection changing standards and protocols. These CD/DVD players, telematics, and is increasingly difficult, as carmakers market characteristics are just the opposite infotainment systems around the globe adopt different solutions. of the relatively long design cycles of tradi- • Under the hood – antilock brakes, tional in-car electronics, which are often emission control, power train, and Electronics Drives Innovation dictated by safety and tooling-cost consid- transmission systems In-car electronics have grown tremendous- erations. ly in recent years. Traditional body-control Traditional systems such as CAN (con- • Advanced safety systems – brake-by- and engine-management functions, plus troller area network) and J1850 have been wire, steer-by-wire, and driver assis- new driver-assistance and telematics sys- used in body control for many years. But tance systems (active safety). 00 Xcell Journal Winter 2004 Figure 1 shows the relative speeds of the LIN network with higher-level networks Media Oriented System Transport various bus systems, which range from such as a CAN bus, extending the benefits MOST networks connect multiple devices, kilobits per second to gigabits per second. of networking all the way to the individual including car navigation, digital radios, dis- sensors and actuators. plays, cellular phones, and CD/DVDs. “Under-the-Hood” Buses MOST technology is optimized for use Two networks found under the hood serve Entertainment and with plastic optical fiber. It supports data functions ranging from seat adjustment to Driver Information Systems rates as high as 24.8 Mbps and is highly antilock brakes. Car infotainment and telematics devices, reliable and scalable at the device level. especially car navigation systems, require MOST offers full support for real-time Controller Area Network highly functional operating systems and audio and compressed video. It is vigorous- One of the first and most enduring control connectivity. Until now, both open-stan- ly supported by German automakers and networks, the CAN bus, is the most widely dard and proprietary standalone buses have suppliers. The MOST bus is endorsed by used, with more than 100 mil- BMW, DaimlerChrysler, lion nodes installed worldwide. Harman/Becker, and OASIS A typical vehicle integrates 1394b 3.2 Gbps High Speed Silicon Systems. A recent two or three CAN buses oper- notable example of a MOST ating at different speeds. A low- IDB-1394 implementation is its use by speed CAN bus runs at less 1394a 400 Mbps Harman/Becker in the latest than 125 Kbps and manages BMW 7 series. body-control electronics, such MOST 45 Mbps as seat and window movement TTP 25 Mbps Intelligent Transport controls and other simple user D2B System Data Bus interfaces. A high-speed (up to FlexRay/byteflight 10 Mbps The IDB Forum manages the 1 Mbps) CAN bus runs real- IDB-C and IDB-1394 buses TTCAN time critical functions such as 1 Mbps and standard interfaces for GM-LAN High Speed engine management, antilock OEMs that develop aftermar- IDB-C CAN 1 Mbps – 50 Kbps brakes, and cruise control. ket and portable devices. CAN protocols are becom- Safe-by-Wire 150 Kbps Based on the CAN bus, IDB- GM-LAN Low/Mid Speed ing standard for under-the- LIN <20 Kbps Low Speed C is geared toward devices hood connectivity in cars, with data rates of 250 Kbps. trucks, and off-road vehicles. IDB-1394 (based on the One outstanding feature of the Figure 1 – In-car network data-transfer speeds IEEE-1394 FireWire™ stan- CAN protocol is its high trans- dard) is designed for high- mission reliability. coexisted independently and peacefully. speed multimedia applications. IDB-1394 But because of the pressures of conver- is a 400 Mbps network using fiber-optic Local Interconnect Network gence, future systems will require integrat- technology. Applications include DVD and The local interconnect network (LIN) was ed electronic subsystems. CD changers, displays, and audio/video developed to supplement the CAN bus in By relying on open industry standards, systems. applications where cost is critical and data all key players – from manufacturers to IDB-1394 also allows 1394-portable transfer rates are low. The LIN bus is an service centers to retailers – can focus on consumer electronic devices to connect and inexpensive serial bus used for distributed delivering core expertise to the customer. interoperate with an in-vehicle network. body control electronic systems. It enables Open standards will save the duplication Zayante Inc., for example, supplies 1394 effective communication for smart sensors of time and effort it would take to devel- physical layer devices for the consumer and actuators where the bandwidth and op separate, incompatible designs for spe- market. A recent joint demonstration with versatility of the CAN bus are not required. cific vehicles or proprietary computing the Ford Motor Company included plug- Typical applications are door control (win- platforms. and-play connections of a digital video dows, door locks, and mirrors), seats, cli- Several organizations and consortia are camera and a Sony PlayStation™ 2 game mate regulation, lighting, and rain sensors. leading standardization efforts, including console, as well as two video displays and a The LIN bus is a UART-based, single- the MOST (Media Oriented System DVD player. master, multiple-slave networking architec- Transport) Cooperation, the IDB ture originally developed for automotive (Intelligent Transport System Data Bus) Digital Data Bus sensor and actuator networking applica- Forum, and the Bluetooth™ Special The Digital Data Bus (D2B) is a network- tions. The LIN master node connects the Interest Group (SIG). ing protocol for multimedia data commu- Winter 2004 Xcell Journal 00 nication that integrates digital audio, that for consumer products or mobile FlexRay standard for next-generation video, and other high-data-rate synchro- phones, so silicon manufacturers must applications. nous or asynchronous signals. It can run as address this mismatch between support The FlexRay system is more than a fast as 11.2 Mbps and be built around and service timescales. On the other hand, communications protocol. It also includes either SmartWire™ unshielded twisted Chrysler showed Bluetooth connectivity in a specially designed high-speed transceiver pair cable or a single optical fiber. its vehicles at Convergence 2002. and the definition of hardware and soft- This communication network is being Some feel Bluetooth technology may be ware interfaces between various compo- driven by C&C Electronics in the UK and overkill in the car environment, however. nents of a FlexRay “node.” The FlexRay has industry acceptance from Jaguar and So, an emerging standard for low data rate protocol defines the format and function of Mercedes-Benz. The integrated multime- wireless data transfer and control has the communication process within a net- dia communication systems deployed in entered the scene. The ZigBee™ wireless worked automotive system. It is designed the Jaguar X-Type, S-Type, and new XJ networking solution is a low-data-rate (868 to complement CAN, LIN, and MOST Saloon, for example, use D2B. MHz to 2.4 GHz), low-power, low-cost networks. The D2B optical multimedia system is system pioneered by Philips. The ZigBee As a scalable system, FlexRay technolo- designed to evolve in line with new tech- range is up to 75 meters and is equally at gy supports both synchronous and asyn- nologies while remaining backwards com- home in industrial control, home automa- chronous data transmission. The patible. D2B optical is based on an open tion, consumer, and possibly automotive synchronous data transmission enables architecture that simplifies expansion, applications. time-triggered communication to meet the because changes to the cable harness are requirement of dependable systems. not required when adding a new device or Advanced Safety Systems FlexRay’s synchronous data transmission is function to the optical ring. The bus uses Safety equipment has evolved from the deterministic, with guaranteed minimum just one polymer optical fiber to handle physical to the electronic domain, starting message latency and message jitter. It sup- the in-car multimedia data and control with advancements in tire and braking ports redundancy and fault-tolerant dis- information. This gives better reliability, technology, through side impact protection tributed clock synchronization to keep the fewer external components and connec- and airbags, and on to today’s driver-assis- schedule of all network nodes within a tors, and a significant reduction in overall tance systems.