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26th International Spring Semin ar on Electronics TechnologyMay 8 - 11,2003, Sta ri Lesni, Slovak Republic

Integrating Sensor Devices in a LIN bus networkAssist.Prof.Chindris Gabriel, Lecturer Hedesiu Horia, Ph.D.

Applied Electronics DeparrmentTechnical University of Cluj-Napoca

G.Baritiu Street 22-24,3400 Cluj-Napoca, RomaniaPhone: +40-264-194806,e-mail gabriel.chindris@ael.utcluj.ro

AbstractThe automotive industry communip as a low-cost network complementing the existing automotive multiplexnetwork has established the LIN standard. The LIN network consisting in a single wire (up to Om), single-master. multiple-slaves and speed up to 19.2Kbps represents an e f f r i e n t alternativefor integrating sensors ina low-cost byT archi tecture. Implemenration of the LIN bus implies the addition of specifc hardware to thesensor design or, additional software leoding to significant CPU overhead (40% or more). Thepaperpresentsa new approach to this implemenration by using System-on-Chip devices. The pro pos ed implementation notonly includes the sensorS signal conditioning hardware but also the specific LIN hardware. Mare than that,wi ng the re-configurabilify feature of the System-an-Chip devices. theproposed design will be able f a changeits hardwarefor different sewors orfor LIN master orLINslave configurations.

1. INTRODUCTIONLIN (Local Interconnect Network) is a new low

cost serial communication system intended to be usedfor distributed electronic systems in vehicles, whichcomplements the existing portfolio of automotivemultiplex networks. LIN is a holistic communicationconcept for local interconnect networks in vehicles.The specification covers in addition to the definitionof the protocol and the physical layer also thedefinition of interfaces for development tools andapplication software. UART interfaces are available aslow cost silicon module on almost all micro-controllerand can also be implemented as equivalent in softwareor pure state machine for ASICs. The medium accessin a LIN network is controlled by a master node sothat no arbi-tmtion or collision management in theslave nodes is required, thus giving a guarantee of theworst-case latency times for signal transmission.

A particular feature of LIN is the synchronizationmechanism that allows the clock recovery by slavenodes without quartz or ceramics resonator. Thespecification of the line driver and receiver isfollowing the I S 0 9141 single-wire standard withsome enhancements. The maximum transmissionspeed is 20 kbit/s, resulting from the requirements byelectromagnetic compatibility (EMC) and clocksynchronization.[ ]

CommunicationConceptA LIN network comprises one master node and

one or more slave nodes. All nodes include a slavecommunication task that is split in a transmit and areceive task, while the master node includes anadditional master transmit task.The communication in

active LIN network is always initiated by themaster task as illustrated in the figure below: themaster sends out a message header which comprisesthe synchronization break, the synchronization byte,and the message identifier. Exactly one slave task isactivated upon reception and filtering of the identifierand starts the transmission of the message response.The response comprises two, four, or eight data bytesand one checksum byte. The header and the responsepart form one message frame.[l]

r 1

Fig. 1 LIN message frame.

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26th Internation al Spring Sem inar on Eleetrnnics TechnologyMay 8 - 11,2003, Star6 Lesna, Slovak Republic

The identifier of a message denotes the content ofa message but not the destination. This communicationconcept enables the exchange of data in various ways:from the master node (using its slave task) to one ormore slave nodes, and from one slave node two themaster node andlor other slave nodes. It is ,possible tocommunicate signals. directly from slave to slavewithout the need for routing through the master node,or broadcasting messages from the master to all nodesin a network. The sequence of message frames iscontrolled by the master and may form cyclesincluding branches.

The LIN specification covers the transmissionprotocol, the transmission medium, the interfaces fordevelopment tools, and application software. LINguarantees the interoperahility of network nodes fromthe viewpoint of hardware and software, and apredictable EMC behavior.

This concept allows the implementation of aseamless chain of development and design tools andenhances the speed of development and the reliabilityof the network.The key features of LIN are[lj:

- Low cost single-wire implementation- Enhanced IS0 9141, VBAT-Based- Speed up to 2OKbiVs- Acceptable speed for many applications

(limited for EMI-reasons)Single Master I Multiple Slave ConceptLow cost silicon implementation based oncommon UARTISCI interface hardware- Almost any microcontroller has necessaryhardware on chip

- Self-synchrnnization in the slave nodeswithout crystal or ceramics resonator

- Significant cost reduction of hardwareplatform

- Guaranteed latency times for signaltransmission- Predictable systems possible

-- No arbitration necessary-

2. LIN SENSORNETWORKSSensor networks have come a long way since thefust point-to-point analog system. Tomorrows

networks will not be dominated by one architecture,but will integrate a variety of networking schemes.Now World Wide Web browsers and object-orientedprogramming techniques are shaping the nextgeneration of networks.[Z]

Over the past few generations, networkingtechnology has edged out of the purely networkingarena to support the needs of the application more

closely. Just as the microcontroller packaged themicroprocessor with common peripherals, todaysnetworks are being enhanced with their equivalents ofapplication-level functionality. Sensor networkingtechnology development has climbed the laye? of theIS0 architecture, and the focus of the future is abovethe I S 0 model, in Layer &the application.

Today, you can find more than 60 different sensornetwork protocols geared for a broad spectrum ofindustries, providing varying degrees of functionalityand success. With the maturation of networkingtechnology, you can choose any one of a half dozenprotocols to build a networked sensor application. Thechoice of which protocol to use is not dictated somuch by the technical features of the protocol as byother considerations, such as the protocolscompatibility witha particular network technology orthe availability of an application or software packagewith that technology. The problem you will face in thenear future is not going to be which network tochoose, but how to cost-effectively support multiplenetworks.Sensor network fopologies

Todays luxury vehicles use more than 80microcontroller-based electronic control units (ECUs)to enhance safety, performance, and convenience. Asthe next generation of automotive control systemstakes advantage of advanced electronics, more sensorswill be needed. To make the most of these sensors,manufacturers will have to come up with a new .approach to system design.

Fig. 2 Automotivesensor network mplementation.In most cases, new designs dont start with a clean

sheet of paper. Instead, designers often create them bynetworking existing systems to share data originatingfrom sensors. The additional sensor inputs can be usedfor sensor fusion and second guessing. For example,the pedal travel sensor may be connected to the power-train ECU, and the information is shared with the ABSECU via a serial communications link. The wheel-speed data generated in the ABS ECU may also beshared with the navigation ECU (as a backup forposition information if the GPS signal is lost).

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26th International Spring Seminar on Electronics TechnologyMay 8- 11,2003, StarA LesnA, S lovak Republic

3. PSoC MPLEMENTATION OF LlN CONTROLLERSDue to the single master and multiple slave

network organization, LIN slaves represent a moreimportant population of the network than LlN masters.However, our implementation aims to design bothconfigurations in the same PSoC chip by takingadvantage of the reconfigurability feature of the chip.It is common knowledge that if system designers canreuse proven hardware and software, they can

Fig 3. Automotive sensornehvork connections

Backbonewim stubs (workable)

Backbonewitn star; or duster; (avoid)

Ring (avoid)

Daisy chain (best)Fig. 4 Network topologies,

significantly reduce development time and costs. Ourimplementation will show how you can reduce costsby using the same hardware for both master and slavedevices.

Figure 5 represents a LIN slave node, with theRxD and TxD PSoC terminals directly connected tothe LIN transceiver.

IIIIII

regulatorI

I GNDI -- - - - - - - - - - - - - - - A

Fig. 5 LIN slave moduleA node in LIN networks does not make use of anyinformation about the system configura tion, except for

the denomination of the master node. Nodes can beadded to the LIN network without requiring hardwareor software changes in other slave nodes. The size o f aLIN network is typically under 12 nodes (though notrestricted to this), resulting from the small number of64 identifier and the relatively low transmission speed.The clock synchronization, the simplicity of UARTcommunication, and the single-wire medium are themajor factors for the cost efficiency of LIN.

Another problem is that each sen sor will generate adifferent output signal (the sensors will likely be fromdifferent suppliers), and there are no interfacestandards in vehicle sensor communications. So eachsensor will require its own analog interface. Be causeit isnt efficient from a cost or space standpoint to useindividual analog interface circuits for each sensor,vehicle manufacturers often use a single analog chipthat contains interfaces for many of the analog inputs.Defining the analog interface chip is difficult becauseof differences between sensor suppliers, specifications,and system details. In short, asmore sensors are used,it becomes more difficult to effic iently implement theanalog interfacing circuits.

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26th Internationa l Spring Seminar on Electronics TechnologyMay 8 - 11,2003, Stara Lesni , Slovak Republic

In this respect, our implementation aims tointegrate altogether also the analog signal conditioningcircuitry required for sensor direct connection.

; PSOC mnMller I

Fig. 6 Integrating the analog part.The PSoC inside design consists in three

LIN slave configuration: analog signalconditioning circuitry (ProgrammableGain Amplifier, Analog to DigitalConverter, intemal calibration andadjusting routines) and LIN slavecommunication module (based on a serialcommunication implementation).LIN master configuration: LIN mastercommunication module (based on a serialcommunication block), LIN bus protocol

configuration tables implemented in flash area:

4. CONCLUSIONSOur LIN masterlslave implementation enables a

cost-effective communication for smart sensors andactuators where the bandwidth and versatility of CANis not required. The communication is based on theSCI WART) data format, a single-master/multiple-slave concept, a single-wire 12V bus, and blocksynchronization for nodes without stabilized timebase. More than that, using the dynamicreconfiguration feature of the PSoC devices, we areable to change the masterlslave configuration via aRS-232 simple interface. The reconfiguration featureis also very useful in disposing unnecessary hardware(analog conditioning circuitry inside PSoC) when thecontroller occupancy needs increases in the LINmaster mode.

Many people are beginning to recognize thatsensor-networking choices are strategic decisions.Companies will change from traditional point-to-pointwiring to less expensive multidrop cabling, realizingthat distributed intelligence at end nodes providesgreater flexibility and modularity. But most peoplewill be unwilling to pay for network integration. Thechallenge for the sensor industry will be to find waysof dealing with competing, functionally overlappingnetwork technologies. [Z]

routines, external link module ( R S 232)for PC connection;Service configuration: designed for [I ] **I LE4 us standard architecture"-www.lin-subbus.org switching the running configuration (LINmaster or L M slave) and for variousadjustment routines.

[2 ] lay Wanior Smart SensorNetwork of he FuNn - Sensor[3] Frank BerberDynamicRcconfi-tion- Cypress

odiacMWanne.MarcbZWoAplioationNote AN2104

141Philippz LarcherDesigning a compactand f lexibibcontmlld-Cyllrcss AplicationNote AN2045 :LIN

Fig. 7 Practical implementation ofLISmasterlslave module.

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