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
`Automotive Product Manager
`Xilinx, Inc.
`karen.parnell@xilinx.com
`
`The next few years will be a rocky road for
`automobile electronics designers. No sin-
`gle in-car data bus can adequately handle
`the entertainment, safety, and intelligent-
`control requirements of the cars that will
`roll off assembly lines in North America,
`Europe, and Asia.
`Choosing the right data bus can lead to
`a competitive advantage, but the selection
`is increasingly difficult, as carmakers
`around the globe adopt different solutions.
`
`Electronics Drives Innovation
`In-car electronics have grown tremendous-
`ly in recent years. Traditional body-control
`and engine-management functions, plus
`new driver-assistance and telematics sys-
`
`00
`
`Xcell Journal
`
`tems, have spurred annual growth rates as
`high as 16%, according to the Institute of
`Electrical and Electronics Engineers
`(IEEE). The IEEE forecasts that electron-
`ics will account for 25% of the cost of a
`mid-size car by 2005.
`One high-growth area is telematics sys-
`tems – the convergence of mobile telecom-
`munications and information processing
`in cars. Significantly, telematics applica-
`tions exhibit market characteristics similar
`to those of consumer products: short time
`to market, short time in market, and
`changing standards and protocols. These
`market characteristics are just the opposite
`of the relatively long design cycles of tradi-
`tional in-car electronics, which are often
`dictated by safety and tooling-cost consid-
`erations.
`Traditional systems such as CAN (con-
`troller area network) and J1850 have been
`used in body control for many years. But
`
`bandwidth and speed restrictions make it
`difficult for these serial, event-driven buses
`to handle newer real-time applications.
`A number of new bus standards have
`emerged featuring time-triggered protocols
`and optical data buses. These in-car bus net-
`works can be divided into four categories:
`
`• Body control – dashboard/instrument
`panel clusters, mirrors, seat belts, door
`locks, and passive airbags
`
`• Entertainment and driver-information
`systems – radios, Web browsers,
`CD/DVD players, telematics, and
`infotainment systems
`
`• Under the hood – antilock brakes,
`emission control, power train, and
`transmission systems
`
`• Advanced safety systems – brake-by-
`wire, steer-by-wire, and driver assis-
`tance systems (active safety).
`
`Winter 2004
`
`

`

`Media Oriented System Transport
`MOST networks connect multiple devices,
`including car navigation, digital radios, dis-
`plays, cellular phones, and CD/DVDs.
`MOST technology is optimized for use
`with plastic optical fiber. It supports data
`rates as high as 24.8 Mbps and is highly
`reliable and scalable at the device level.
`MOST offers full support for real-time
`audio and compressed video. It is vigorous-
`ly supported by German automakers and
`suppliers. The MOST bus is endorsed by
`BMW,
`DaimlerChrysler,
`Harman/Becker, and OASIS
`Silicon Systems. A recent
`notable example of a MOST
`implementation is its use by
`Harman/Becker in the latest
`BMW 7 series.
`
`High Speed
`
`LIN network with higher-level networks
`such as a CAN bus, extending the benefits
`of networking all the way to the individual
`sensors and actuators.
`
`Entertainment and
`Driver Information Systems
`Car infotainment and telematics devices,
`especially car navigation systems, require
`highly functional operating systems and
`connectivity. Until now, both open-stan-
`dard and proprietary standalone buses have
`
`IDB-1394
`
`1394b
`
`3.2 Gbps
`
`1394a
`
`400 Mbps
`
`MOST
`
`45 Mbps
`
`TTP
`
`D2B
`FlexRay/byteflight
`
`25 Mbps
`
`10 Mbps
`
`TTCAN
`
`1 Mbps
`
`Figure 1 shows the relative speeds of the
`various bus systems, which range from
`kilobits per second to gigabits per second.
`
`“Under-the-Hood” Buses
`Two networks found under the hood serve
`functions ranging from seat adjustment to
`antilock brakes.
`
`Controller Area Network
`One of the first and most enduring control
`networks, the CAN bus, is the most widely
`used, with more than 100 mil-
`lion nodes installed worldwide.
`A typical vehicle integrates
`two or three CAN buses oper-
`ating at different speeds. A low-
`speed CAN bus runs at less
`than 125 Kbps and manages
`body-control electronics, such
`as seat and window movement
`controls and other simple user
`interfaces. A high-speed (up to
`1 Mbps) CAN bus runs real-
`time critical functions such as
`engine management, antilock
`brakes, and cruise control.
`CAN protocols are becom-
`ing standard for under-the-
`hood connectivity
`in cars,
`trucks, and off-road vehicles.
`One outstanding feature of the
`CAN protocol is its high trans-
`mission reliability.
`
`GM-LAN High Speed
`IDB-C
`
`CAN
`
`Safe-by-Wire
`GM-LAN Low/Mid Speed
`LIN
`
`1 Mbps – 50 Kbps
`150 Kbps
`<20 Kbps
`
`Low Speed
`
`Figure 1 – In-car network data-transfer speeds
`
`coexisted independently and peacefully.
`But because of the pressures of conver-
`gence, future systems will require integrat-
`ed electronic subsystems.
`By relying on open industry standards,
`all key players – from manufacturers to
`service centers to retailers – can focus on
`delivering core expertise to the customer.
`Open standards will save the duplication
`of time and effort it would take to devel-
`op separate, incompatible designs for spe-
`cific vehicles or proprietary computing
`platforms.
`Several organizations and consortia are
`leading standardization efforts, including
`the MOST (Media Oriented System
`Transport) Cooperation,
`the
`IDB
`(Intelligent Transport System Data Bus)
`Forum, and the Bluetooth™ Special
`Interest Group (SIG).
`
`Local Interconnect Network
`The local interconnect network (LIN) was
`developed to supplement the CAN bus in
`applications where cost is critical and data
`transfer rates are low. The LIN bus is an
`inexpensive serial bus used for distributed
`body control electronic systems. It enables
`effective communication for smart sensors
`and actuators where the bandwidth and
`versatility of the CAN bus are not required.
`Typical applications are door control (win-
`dows, door locks, and mirrors), seats, cli-
`mate regulation, lighting, and rain sensors.
`The LIN bus is a UART-based, single-
`master, multiple-slave networking architec-
`ture originally developed for automotive
`sensor and actuator networking applica-
`tions. The LIN master node connects the
`
`Winter 2004
`
`Intelligent Transport
`System Data Bus
`The IDB Forum manages the
`IDB-C and IDB-1394 buses
`and standard interfaces for
`OEMs that develop aftermar-
`ket and portable devices.
`Based on the CAN bus, IDB-
`C is geared toward devices
`with data rates of 250 Kbps.
`IDB-1394 (based on the
`IEEE-1394 FireWire™ stan-
`dard) is designed for high-
`speed multimedia applications. IDB-1394
`is a 400 Mbps network using fiber-optic
`technology. Applications include DVD and
`CD changers, displays, and audio/video
`systems.
`IDB-1394 also allows 1394-portable
`consumer electronic devices to connect and
`interoperate with an in-vehicle network.
`Zayante Inc., for example, supplies 1394
`physical layer devices for the consumer
`market. A recent joint demonstration with
`the Ford Motor Company included plug-
`and-play connections of a digital video
`camera and a Sony PlayStation™ 2 game
`console, as well as two video displays and a
`DVD player.
`
`Digital Data Bus
`The Digital Data Bus (D2B) is a network-
`ing protocol for multimedia data commu-
`
`Xcell Journal
`
`00
`
`

`

`nication that integrates digital audio,
`video, and other high-data-rate synchro-
`nous or asynchronous signals. It can run as
`fast as 11.2 Mbps and be built around
`either SmartWire™ unshielded twisted
`pair cable or a single optical fiber.
`This communication network is being
`driven by C&C Electronics in the UK and
`has industry acceptance from Jaguar and
`Mercedes-Benz. The integrated multime-
`dia communication systems deployed in
`the Jaguar X-Type, S-Type, and new XJ
`Saloon, for example, use D2B.
`The D2B optical multimedia system is
`designed to evolve in line with new tech-
`nologies while remaining backwards com-
`patible. D2B optical is based on an open
`architecture that simplifies expansion,
`because changes to the cable harness are
`not required when adding a new device or
`function to the optical ring. The bus uses
`just one polymer optical fiber to handle
`the in-car multimedia data and control
`information. This gives better reliability,
`fewer external components and connec-
`tors, and a significant reduction in overall
`system weight.
`
`Bluetooth and ZigBee
`Bluetooth wireless technology is a low-cost,
`low-power, short-range radio protocol for
`mobile devices and WAN/LAN access
`points. Its specification describes how
`mobile phones, computers, and PDAs can
`easily interconnect with each other, with
`home and business phones, and with com-
`puters.
`The Bluetooth SIG includes such mem-
`bers as AMIC, BMW, DaimlerChrysler,
`Ford, General Motors, Toyota, and
`Volkswagen. An example of Bluetooth
`deployment in cars is Johnson Controls’
`BlueConnect™ technology, a hands-free
`system that allows drivers to keep their
`hands on the wheel while staying connect-
`ed through a Bluetooth-enabled cellular
`phone.
`There is, however, some concern about
`long-term support of Bluetooth devices.
`The problem centers on how the electro-
`magnetically noisy in-car environment will
`affect Bluetooth operation. The lifecycle of
`cars and other vehicles is much longer than
`
`00
`
`Xcell Journal
`
`that for consumer products or mobile
`phones, so silicon manufacturers must
`address this mismatch between support
`and service timescales. On the other hand,
`Chrysler showed Bluetooth connectivity in
`its vehicles at Convergence 2002.
`Some feel Bluetooth technology may be
`overkill in the car environment, however.
`So, an emerging standard for low data rate
`wireless data transfer and control has
`entered the scene. The ZigBee™ wireless
`networking solution is a low-data-rate (868
`MHz to 2.4 GHz), low-power, low-cost
`system pioneered by Philips. The ZigBee
`range is up to 75 meters and is equally at
`home in industrial control, home automa-
`tion, consumer, and possibly automotive
`applications.
`
`Advanced Safety Systems
`Safety equipment has evolved from the
`physical to the electronic domain, starting
`with advancements in tire and braking
`technology, through side impact protection
`and airbags, and on to today’s driver-assis-
`tance systems.
`The latest vehicles are electronics-rich
`and sensor-based to continuously evaluate
`the surroundings, display relevant informa-
`tion to the driver, and, in some instances,
`even take control of the vehicle.
`Advanced safety systems include by-
`wire (for example, drive-by-wire and brake-
`by-wire), which will replace traditional
`hydraulic and mechanical linkages with
`safer, lighter electronic systems.
`Other examples of advanced, real-time
`safety systems include distance control,
`self-adjusting and sensing airbag systems,
`radar parking, reversing aids, and back
`guide monitors (cameras set in the car’s
`bumpers to aid parking).
`
`FlexRay
`The FlexRay™ network communication
`system is aimed at the next generation of by-
`wire automotive applications. These applica-
`tions demand high-speed buses that are
`deterministic, fault-tolerant, and capable of
`supporting distributed control systems.
`BMW, DaimlerChrysler,
`Philips
`Semiconductors, Motorola, and the newest
`member, Bosch, are developing
`the
`
`FlexRay standard for next-generation
`applications.
`The FlexRay system is more than a
`communications protocol. It also includes
`a specially designed high-speed transceiver
`and the definition of hardware and soft-
`ware interfaces between various compo-
`nents of a FlexRay “node.” The FlexRay
`protocol defines the format and function of
`the communication process within a net-
`worked automotive system. It is designed
`to complement CAN, LIN, and MOST
`networks.
`As a scalable system, FlexRay technolo-
`gy supports both synchronous and asyn-
`chronous
`data
`transmission. The
`synchronous data transmission enables
`time-triggered communication to meet the
`requirement of dependable
`systems.
`FlexRay’s synchronous data transmission is
`deterministic, with guaranteed minimum
`message latency and message jitter. It sup-
`ports redundancy and fault-tolerant dis-
`tributed clock synchronization to keep the
`schedule of all network nodes within a
`tight, predefined, precision window.
`The asynchronous transmission, based on
`the fundamentals of the byteflight™ proto-
`col, allows each node to use the full band-
`width for event-driven communications.
`
`Time-Triggered Protocol
`Designed for fault-tolerant, real-time dis-
`tributed systems, the time-triggered proto-
`col (TTP) ensures that there is no single
`point of failure.
`TTP is a mature, low-cost solution that
`can handle safety-critical applications.
`Second-generation silicon supporting com-
`munication speeds as high as 25 Mbps is
`available today. The TTA Group, the gov-
`erning body for TTP, includes Audi, SA,
`Renault, NEC, TTChip, Delphi, and
`Visteon among its members.
`
`Time-Triggered CAN
`The time-triggered CAN (TTCAN) stan-
`dard is an extension of the CAN protocol.
`It adds a session layer on top of the existing
`data link layer and physical layers to ensure
`that all transmission deadlines are met,
`even at peak bus loads. The protocol imple-
`ments a hybrid, time-triggered, TDMA
`
`Winter 2004
`
`

`

`Figure 2 – In-car multimedia functions embedded in an FPGA
`
`(time-division multiplexed access) schedule
`that also accommodates event-triggered
`communications. Some of the intended
`TTCAN uses include engine management
`systems and transmission and chassis con-
`trols, with scope for by-wire applications.
`
`The Programmable Logic Solution
`As we have seen from the proliferating num-
`ber of in-car bus standards, the next few years
`will become a minefield for automotive elec-
`tronics designers. Choosing the right data
`bus will be crucial to success – now measured
`not simply during integration and testing of
`units for production, but long after the car
`has rolled off the assembly line.
`The problem is amplified for Tier 1
`suppliers and aftermarket companies that
`supply units to many OEMs, because
`these customers are likely to opt for differ-
`ent data buses and protocols. The industry
`has seen a huge shift away from designing
`a different unit for every OEM – indeed
`for every car model. Taking its place is a
`design philosophy that emphasizes recon-
`figurable platforms.
`Design platforms that are cleverly parti-
`tioned between software and reprogram-
`mable hardware let manufacturers change
`system buses and interfaces late in the
`
`Winter 2004
`
`design process – and even in production.
`The reconfigurable system concept sup-
`ports try-outs of different standards and
`protocols. Programmable logic devices
`(PLDs) in the form of FPGAs and CPLDs
`enable modification during all phases of
`design – from prototype through pre-pro-
`duction and into production.
`PLDs can also alleviate over-stocking
`and inventory issues, because generic
`FPGAs can be used across many projects
`and are not application-specific. Once the
`programmable logic-based unit is on the
`road, it can even be reconfigured remotely
`via a wireless communication link to allow
`for system upgrades or extra functions.
`
`Drop-In IP Cores
`The reconfigurable hardware platform can
`be brought to market quickly by utilizing
`drop-in intellectual property (IP) core
`blocks. Memec Design, for example,
`recently announced the availability of a
`cost-optimized CAN core interface that
`includes the complete data link layer,
`including the framer, transmit-and-receive
`control, error core design, and flexible
`interface. Bit rate and sub-bit segments can
`be configured to meet the timing specifica-
`tion of the connected CAN bus.
`
`The Memec core is designed to provide
`a bus bit rate of up to 1 Mbps, with a min-
`imum core clock frequency of 8 MHz. It
`can provide an interface between the mes-
`sage filter, the message priority mechanism,
`and various system functions such as sen-
`sor/activator controls.
`Alternatively, the Memec CAN bus can
`be embedded into a system application
`interfacing with the microprocessor and
`various peripheral functions. Another
`example is Intelliga’s iLIN™ core, which is
`supplied as a LIN bus controller IP core. It
`uses a synchronous 8-bit general-purpose
`microcontroller interface with minimal
`buffering to transport message data. In
`addition, the reference design includes a
`single slave message response filter and a
`software interface that allows the connect-
`ed microcontroller to perform address fil-
`tration.
`This emerging LIN body control proto-
`col can be easily tried and tested using the
`Intelliga iDEV prototyping board, which
`can demonstrate not only LIN but also
`CAN and TTCAN buses – all implement-
`ed in a Xilinx Spartan™-IIE FPGA.
`Figure 2 shows a generic in-car multi-
`media system design with a CAN core sup-
`plying communications for a PCMCIA
`
`Xcell Journal
`
`00
`
`

`

`Figure 3 – In-car complementary networks
`
`interface, PCI bridging, an IDE interface,
`and other functions. One printed circuit
`board can be used for many customers with
`customization in the FPGA instead of the
`board. The model can be extended to
`include modification or upgrades in the
`field via wireless connection to reconfigure
`the FPGA in-system.
`
`Bus Coexistence
`Several in-car bus networks can coexist to
`deliver the right combination of data rates,
`robustness, and cost.
`Figure 3 shows the LIN bus handling
`low-cost, low-speed connections between
`the motors for the mirrors, roof, windows,
`and so forth. A CAN bus handles data
`communication and control between the
`instrument cluster, body controllers, door
`locks, and climate control. Finally, the
`high-speed MOST optical bus connects
`the entertainment, navigation, and com-
`munication devices.
`This model can be extended to include
`
`00
`
`Xcell Journal
`
`a FlexRay bus (or other real-time safety
`bus) to handle the high-speed, real-time
`data required by advanced safety systems.
`
`Conclusion
`The delicate engineering balance between
`cost, reliability, and performance has creat-
`ed a variety of emerging in-car bus systems
`that will complicate design decisions for
`years to come. Therefore, automotive
`OEMs are backing more than one standard
`due to uncertainties over which one will
`eventually prevail.
`There is an elegant solution to this
`dilemma. Reconfigurable platforms based
`on Xilinx programmable logic and IP cores
`are the best way out of this design predica-
`ment. Without sacrificing performance or
`cost advantages, reconfigurable hardware
`and software systems from Xilinx allow
`manufacturers to quickly accommodate
`changing standards and protocols late in
`the design process, in production, and even
`on the road.
`
`Website resources
`
`CAN
`
`GM LAN
`
`MOST
`
`www.can.bosch.com
`
`www.gmtcny.com/lan.htm
`
`www.mostnet.de
`
`TTTech (TTP)
`
`www.ttagroup.org, www.ttchip.com
`
`FlexRay
`
`www.flexray.com
`
`D2B
`
`LIN
`
`www.candc.co.uk
`
`www.lin-subbus.org
`
`Intelliga (LIN)
`
`www.intelliga.co.uk
`
`Bluetooth
`
`www.bluetooth.com
`
`IDB
`
`ZigBee
`
`www.idbforum.org
`
`www.zigbee.org
`
`Xilinx Automotive www.xilinx.com/automotive/
`
`Winter 2004
`
`