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`FORD EX. 1015
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`AUTOMOTIVE
`ELECTRONICS
`HANDBOOK
`
`Ronald K. Jurgen Editor in Chief
`
`McGraw-Hill, Inc.
`New York San Francisco Washington, D.C. Auckland Bogota
`Caracas Lisbon London Madrid Mexico City Milan
`Montreal New Delhi San Juan Singapore
`Sydney Tokyo Toronto
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`/
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`FORD EX. 1015
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`Library of Congress Cataloging-in-Publication Data
`
`/ Ronald Jurgen, editor in chief.
`
`Automotive electronics handbook
`p.
`cm.
`Includes index.
`ISBN 0-07-033189-8
`1. Automobiles - Electronic equipment.
`TL272.5.A982
`1994
`629.25'49-dc
`
`I. Jurgen , Ronald K.
`
`94-39724
`CIP
`
`Copyright © 1995 by McGraw-Hill, Inc . All rights reserved. Printed in the
`United States of America . Except as permitted under the United States
`Copyr ight Act of 1976, no part of this publication may be reproduced or dis(cid:173)
`tributed in any form or by any means, or stored in a data base or retrieval
`system, without the prior written permission of the publisher.
`
`1 2 3 4 5 6 7 8 9 0 AGM/AGM
`
`9 0 9 8 7 6 5 4
`
`ISBN 0-07-033189-8
`
`The sponsoring editor for this book was Stephen S. Chapman, the editing
`supervisor was Virginia Carroll, and the production supervisor was
`Suzanne W B. Rapcavage . It was set in Times Roman by North Market
`Street Graphics.
`
`Printed and bound by Arcata Graphics/Martinsburg.
`
`McGraw-Hill books are available at special quantity discounts to use as pre(cid:173)
`miums and sales promotions , or for use in corporate training programs . For
`more information, please write to the Director of Special Sales, McGraw (cid:173)
`Hill, Inc., 11 West 19th Street, New York , NY 10011. Or contact your local
`bookstore .
`
`Information contained in this work has been obtained by McGraw(cid:173)
`Hill, Inc . from sources believed to be reliable. However , neither
`McGraw-Hill nor its authors guarantee the accuracy or complete(cid:173)
`ness of any information published herein , and neither McGraw(cid:173)
`Hill nor its authors shall be responsible for any errors , omissions ,
`or damages arising out of use of this information. This work is
`published with the understanding that McGraw-Hill and its authors
`are supplying information , but are not attempting to render engi(cid:173)
`neering or other professional services . If such services are
`required , the assistance of an appropriate professional should be
`sought.
`
`This book is printed on acid-free paper.
`
`FORD EX. 1015
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`CHAPTER22
`ON- AND OFF-BOARD
`DIAGNOSTICS
`
`Wolfgang Bremer, Frieder Heintz, and Robert Hugel
`Robert Bosch GmbH
`
`22. 1 WHY DIAGNOSTICS?
`
`The desire for greater safety, driving comfort, and environmental compatibility is leading to a
`rapid increase in electronic control units and sensors in upper class, medium-siz ed, and com(cid:173)
`pact vehicles. Additional functions and their corresponding equipment in today's cars create
`a bewildering tangle of cables and confusing functional connections . As a result, it has become
`more and more difficult to diagnose faults in such systems and to resolve them within a rea(cid:173)
`sonable period.
`
`22.1.1 Diagnostics in the Past and Today
`
`On-board diagnosis has been limited thus far to a few error displays and fault storage
`achieved by relatively simple means . It has been left more or less to each manufacturer to
`decide to what extent diagnosis would be carried out. Diagnosis always means the working
`together of man and machine and consists essentially of three major components: registration
`of the actual condition, knowledge of the vehicle and its nominal condition, and strateg y(cid:173)
`how to find the smallest exchangeable deficient component by means of combining and com(cid:173)
`paring both the nominal and actual conditions.
`All three points are inseparably connected . Only the means to the end have changed over
`time. The oldest and simplest method of diagnosis is that done with the help of our sense
`organs, but the limits of this kind of diagnosis are obvious. In fact , the objective in the devel(cid:173)
`opment of diagnostic techniques is the extension of human abilities with the aid of diagnostic
`tools in order to be able to measure more precisely and more directly, to compare more objec (cid:173)
`tively, and to draw definite conclusions .
`The development of control techniques was essentially determined by the following items :
`the development of automotive engineering ; the structure of workshops-that
`is, essentially
`the relation between the costs of labor and materials; and the development of electronics and
`data processing.
`For a long time, motor diagnosis was limited to ignition control and timing. In the 1960s,
`new exhaust -gas measuring instruments for fuel injection adjustment were developed , but the
`mechanic still had to make the diagnosis. In the 1980s, the introduction of electronics in the
`vehicle was followed by a new generation of measuring instruments in the workshops . Not
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`22.1
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`ON-AND OFF-BOARD DIAGNOSTICS
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`22.3
`
`control units and sensors are tied to a diagnostic connector which is plugged into the measur(cid:173)
`ing instrument with a corresponding adapter for the respective vehicle. Because of the per(cid:173)
`manently increasing amount of electronic functions, it is necessary to develop connectors with
`more and more contacts . It is evident that this method soon will become too unwieldy.
`Modern electronics in vehicles support diagnosis by comparing the registered actual val(cid:173)
`ues with the internally stored nominal values with the help of control units and their self-diag(cid:173)
`nosis, thus detecting faults. By interconnecting the measuring instruments , a detailed survey of
`the entire condition of the vehicle is available and an intelligent on-board diagnostic system
`is able to carry out a more precise and more definite localization of the defect. 2 With the help
`of an interconnection and standardization of the interface leading to the external tester, the
`many different complex and expensive adapters have become superfluous . Modern diagnosis
`will look like what is shown in Fig. 22.3.
`
`FIGURE 22.3 Future diagnostic connector installation in a vehicle.
`
`Instead of a multiplicity of adapters there is only a single standardized interface, provided
`by the diagnostic processor. By means of interconnection , the diagnostic processor is provided
`with all available data and the condition of the vehicle is known. With the help of the diag(cid:173)
`nostic processor, the external measuring instrument has access to the measuring and diagnos(cid:173)
`tic values of the sensors and is able to directly reach the actuator for measuring purposes. 3
`Such a diagnosis also demands a certain change in the functional structure of a vehicle .
`Corresponding hierarchical models have already been presented .4
`
`22.1.2 Reasons for Diagnostics in Vehicles
`
`Which are the most important reasons for diagnostics as demanded and desired in today 's
`vehicles?
`
`Existing Diagnostic Problems. A number of diagnostic problems must be resolved:
`
`• Early diagnostic information was related only to single components and control units. In
`case of a defective comprehensive system , every unit , compon ent , sensor , and connecting
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`22.2
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`DISPLAYS AND lNFORMATION SYSTEMS
`
`FIGURE 22.1 Evolution of diagnostic test equipment.
`
`only were separate measurements combined with comprehensive test procedures, but also the
`information about the nominal condition of the vehicle was stored in a data memory. 1 A view
`of the development is shown in Fig. 22.1.
`As more and more electronic systems were added to cars, the more difficult it became to
`determine the actual condition in case of a defect. Soon a multitude of connecting cables and
`adapters were required to reach the necessary measuring points. Moreover there was an
`increasing amount of information needed to make an effective diagnosis. In the majority of
`workshops, diagnosis is carried out as shown in Fig. 22.2. The most important test points of
`
`FIGURE 22.2 Present-day diagnostic connector installation in a vehicle.
`
`22
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`22.4
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`DISPLAYS AND INFORMATION SYSTEMS
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`cable of the system had to be tested and controlled . This was a very time consuming and
`expensive process.
`• Because of the single component and control unit checks, it was impossible to analyze all
`the additional data correlated with a particular defect.
`• In the case of a defect in single sensors or units, the car was often inoperable. Taking into
`consideration all available information about the vehicle, it is possible to use alternative
`parameters and procedures in order to achieve at least a so-called limp-home function and
`sometimes continue the use of the vehicle under only slightly limited operating conditions.
`• Usually there was only a global error display with an often ambiguous warning light avail(cid:173)
`able for the driver. Drivers desire more detailed information and especially guidelines for
`what procedures should be followed.
`• The multitude of adapter cables, plugs, diagnostic equipment , and communication inter(cid:173)
`faces in a workshop has become so complex that the effectiveness decreased dramatically ,
`with the repair costs increasing disproportionally.
`
`New Legal Proposals. Worldwide new legal proposals and governmental regulations [e.g.,
`California Air Resources Board (CARB) , On Board Diagnostics II (OBDII) , Environmental
`Protection Agency (EPA)] are forcing manufacturers and subcontractors to seek more prof(cid:173)
`itable , effective, and convincing diagnosis of vehicles.
`
`Serial Data Networks. New serial data networks for the connection of control units and
`vehicle body components, installed in the vehicle, offer the possibility of absolutely new opti(cid:173)
`mum approaches and even anticipate maintenance and diagnosis up to the introduction of
`6
`7
`8
`autodidactic data processing systems and external data bases.5
`•
`·
`•
`
`International Initiatives for Standardization.
`Initiated by legislative and governmental
`demands for better diagnostics in the area of emission control , initiatives for standardization
`in the entire diagnostic field in vehicles were launched during recent years to achieve world(cid:173)
`wide standardization of tools, interfaces , connectors, and protocols.
`
`22.1.3 Diagnostic Tasks in Vehicles
`
`In order to minimize the number of defects or even to completely avoid them, a vehicle
`requires regular checks. In case of an inevitable defect , a clear and directed diagnosis is
`required and has to be followed by a prompt , reliable , and inexpensive repair. Therefore
`appropriate diagnostic systems are being developed considering the following targets: simpli(cid:173)
`fication of maintenance, fault indication in time, guidelines for the driver in case of a defect,
`and safer and faster repairs with the help of a specific fault indication.
`In addition to technical considerations, environmental aspects are now being taken into
`consideration as reflected in the diagnostic concepts. In the future, only perfect systems will
`be accepted , in order to keep environmental pollution to a minimum. It is understandable ,
`therefore , that legislators insist on increased monitoring standards, particularly for exhaust(cid:173)
`related components.
`As an example of the new monitoring standards , consider the requirements of CARB
`and EPA in the United States and the resulting consequences for diagnosis . At the moment ,
`the extent of such a detailed monitoring has to be a compromise between the different
`requirements and the possible technical and economical solutions , but the environmental
`aspects will gain more and more importance . The increased amount of available data will
`certainly permit a considerably higher rate of in-depth fault localization and will also allow
`clear fault identification without interactive outside intervention. Having knowledge of the
`functional interrelationships and access to all essential data , a picture of the defect can be
`created with the help of individual pieces of information . The driver and the workshop can
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`ON-AND OFF-BOARD DIAGNOSTICS
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`22.5
`
`then be provided with appropriate instructions. In this context , on-board expert systems are
`being considered.
`For an effective and successful diagnosis today and in the future the following tasks and
`targets can be defined.
`
`Fault Storage with Boundary Conditions. A very important aspect of modern diagnosis is
`the clear and reliable analysis of the respective fault . During the self-diagnosis, it is absolutely
`necessary to store not only the respective fault information but also all relevant marginal
`parameters in the control unit, e.g., ambient temperature, velocity, engine speed, engine
`knock, and so on. The additional data can be stored when a defect occurs as well as during
`specified intervals around the moment of a defect. Such additional data is called "freeze
`frame" data. 9
`
`Fault Localization. Mechanics must be able to locate a defective control unit quickly and
`then determine which component of that control unit is at fault so that it can be replaced.
`
`Data Correlation, Recognition of Imminent Faults. A large amount of data useful for the
`analysis of a vehicle is now available and even more will be available in the future. These data
`will have to be evaluated and compared with the help of modern data processing techniques ,
`including fuzzy logic, neural networks, autodidactic systems, and expert systems. These tech(cid:173)
`niques will not only enable the diagnosis of the actual condition of the vehicle but will also
`determine future maintenance needs . As a result, the reliability and availability of a vehicle
`will be increased and the possible consequences of a defect kept to a minimum. The driver can
`also be forewarned about imminent problems and can then take appropriate steps before
`starting on a trip.
`
`Parameter Substitution. The breakdown of a sensor in modern diagnostic procedures is not
`necessarily followed by a lack of the respective information. After having diagnosed a fault, the
`diagnostic computer-with
`the aid of the available information-is often able to compute an
`auxiliary parameter to replace the original one. As a result, either a limp-home condition is pos(cid:173)
`sible or else the nominal function can be assured but under slightly limited conditions. Simple
`examples for such a calculated parameter are vehicle speed ( considering the gear and the syn(cid:173)
`chronous speed, or the antilock braking information , or the data of the navigation system), motor
`temperature (considering the outside temperature and the operating time), and the amount of
`remaining fuel (considering the last actual fuel content and the calculated consumption) .
`
`Providing Guidelines. As mentioned earlier , a diagnostic system has to provide clear infor(cid:173)
`mation to the driver in case of a defect. A global warning indication is not sufficient. The
`driver needs to learn the extent of the defect and its consequences by appropriate text , graph(cid:173)
`ics, or synthetic voice. In addition, the driver needs to be told the steps that have to be taken
`(e.g., "refill cooling water," "minimum speed to the next service station , risk of engine break(cid:173)
`down," "stop , brake system out of order"). 10
`
`The diagnostic monitoring system can also be used , if there is no service station nearby , as
`a substitutional off-board system. The defect is then localized by an interactive working
`together of the indicating system and an appropriate input medium .
`
`External Diagnostic Access. For off-board diagnosis, the diagnostic system of the vehicle
`has to provide a standardized access to all relevant components, control units, and stored
`information . This standardized access might also be used by the vehicle manufacturer , legisla-
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`22.6
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`DISPLAYS AND INFORMATION SYSTEMS
`
`tor , application engineer, and the end-of-the-line programmer. The access itself has to be con(cid:173)
`trolled with the help of an appropriate mechanism to prevent possible abuse .11
`
`Logbook Function. The control unit or the diagnostic computer of the vehicle is supposed
`to store every repair that has been carried out in the format of a logbook . It should contain
`the time and name of the workshop, every exchanged and newly installed element , every
`inspection carried out , and so forth.
`
`22.2 ON-BOARD DIAGNOSTICS
`
`The more complex automobiles became , the greater the number of electronic systems and the
`more difficult became the registration of the actual condition in case of a defect. To reach the
`necessary measuring points , many connecting cables and adapters were required . In addition,
`much data about the different systems and their working together was needed to allow a sys(cid:173)
`tem-specific diagnosis. Modern electronics with self-diagnosis supports the service mechanic
`by registrating the actual values, comparing them with the nominal values, and diagnosing
`faults that are stored for repair purposes . Actually, the internal functions are checked when (cid:173)
`ever an ECU is turned on.
`First, the checksum of the program memory is checked together with its function and the
`correct version . Then a read and write test of the RAM cells is performed. Special peripheral
`elements ( e.g., AD converters) are also checked within this test cycle. During the entire oper(cid:173)
`ating time of the vehicle, the ECUs are constantly supervising the sensors they are connected
`to. With the help of an adequate interpretation of the hardware , controllers are able to deter (cid:173)
`mine whether a sensor has a short circuit to ground or battery voltage, or if a cable to the sen(cid:173)
`sor is interrupted. By comparing the measured values and the stored technical data , a
`controller is able to determine whether the measured values exceed the limits, drift away, or
`are still within the tolerable limits. The combination of information provided by other sensors
`allows the monitoring for plausibleness of the measured values.
`Sensors are tested similarly to the way actuators are monitored for short circuits or inter (cid:173)
`ruptions of cables. The check is carried out by measuring the electric current or reading the
`diagnostic output of intelligent driver circuits. The function of an actuator under certain con(cid:173)
`ditions can be tested by powering the actuator and observing the corresponding reaction of
`the system . If discrepancies to the nominal values are diagnosed , the information is stored in
`an internal fault memory together with relevant outside parameters , e.g., the motor tempera (cid:173)
`ture or the engine speed . Thus, defects that appear once or under certain conditions can be
`diagnosed. If a fault occurs only once during several journeys , it is deleted . The fault memory
`can be read later in the workshop and provides valuable information for the mechanic.
`In case of a detected defective sensor, the measured values are replaced by nominal values
`or an alternative value is formed using the information of other sensors to provide at least a
`limp-home function.
`With the help of an appropriate interface, a tester can communicate with the ECUs, read
`the fault memory and the measured values , and send signals to the actuators. In order to be
`able to use self-diagnosis as universally as possible, manufacturers aim at the standardization
`of the interface and the determination of appropriate protocols for data exchange.
`Another task of self-diagnosis is the indication of a defect to the driver. Faults are mostly
`indicated by one or more warning lights on the dashboard. Modern developments aim at
`more comprehensive information using displays for text and graphics , which provide priority(cid:173)
`controlled information for the driver. Legal regulations concerning exhaust-gas gave rise to
`an essential extension of self diagnosis. The control units have to be able to control all
`exhaust-relevant functions and components and to clearly indicate a defective function or the
`exceeding of the permissible exhaust limits. Some of the demanded functions require an enor -
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`CHAPTER26
`MULTIPLEX WIRING SYSTEMS
`
`Fred Miesterfeld
`Chrysler Corporation
`
`26. 1 VEHICLE MULTIPLEXING
`
`Production and proposed passenger vehicle multiplexing and data communications network
`systems will be thoroughly examined in this chapter. The systems covered are those methods
`that are relevant to the electronic engineer who has the assignment of applying multiplexing
`techniques to high-volume production. In passenger vehicle design, cost is the universal
`method of determining whether or not a design will be put into production. If a multiplex net(cid:173)
`work design can be applied while delivering functional improvements at a system-cost saving,
`then this design is the most likely network design to be accepted .
`The SAE Vehicle Network for Multiplexing and Data Communications (Multiplex) Com-
`mittee has defined 1 three classes of vehicle data communication networks:
`
`Class A. A potential multiplex system usage where vehicle wiring is reduced by the trans(cid:173)
`mission and reception of multiple signals over the same signal bus between nodes that
`would have ordinarily been accomplished by individual wires in a conventionally wired
`vehicle. The nodes used to accomplish multiplexed body wiring typically did not exist in
`the same or similar form in a conventionally wired vehicle.
`Class B. A potential multiplex system usage where data ( e.g., parametric data values) are
`transferred between nodes to eliminate redundant sensors and other system elements. The
`nodes in this form of a multiplex system typically already existed as stand-alone modules
`in a conventionally wired vehicle.
`'
`Class C. A potential multiplex system usage where high data rate signals, typically asso(cid:173)
`ciated with real-time control systems, such as engine controls and antilock brakes, are sent
`over the signal bus to facilitate distributed control and to further reduce vehicle wiring.
`
`The Class B network is intended to be a functional superset of the Class A network; i.e., the
`Class B bus must be capable of communications that would perform all of the functions of a
`Class A bus. This feature protects the use of the same bus for all Class A and Class B functions
`or an alternate configuration of both buses with a gateway device. In a similar manner, the
`Class C bus is intended as a functional superset of the Class B bus.
`Generally, this section will deal only with the requirements for the lowest three layers of
`the seven-layer ISO open system interconnects (OSI) model (Ref. ISO 7498). These layers in
`descending order are the network layer, data link layer, and the physical layer.
`
`26.1
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`26.2
`
`SAFETY , CONVENIENCE , ENTERTAINMENT ,AND OTHER SYSTEMS
`
`26.1.1 Background of Vehicle Network Architectures
`
`A wide variety of network topologies 2 can be envisioned by network designers. The message
`structure described in this section is very flexible and useful in exchanging information
`between network nodes. The following discussion describes two network architectures which
`are likely configurations that can use this message definition set: a single-network architec(cid:173)
`ture and a multiple-network architecture.
`The selection would be application-specific and, thus , it is the system designer's choice as
`to which network architectures to use. It should be noted that the hardware that supports
`these two message structures is generally not interchangeable . It is recommended that care be
`taken in choosing which message definition to use, because the selection is generally irre (cid:173)
`versible because of hardware limitations .
`
`Header Selection. The header field (header) is a one- , two-, or three-byte field within a
`frame and contains information about the message priority, message source, target address ,
`message type, and in-frame response . The multiple network architecture is usually associated
`with the single-byte header protocol. Figure 26.1 (1) illustrates the header byte as the message
`identifier (ID), which is primarily used for functional "broadcast "-type messages and implic(cid:173)
`itly defines all the required information about the message . It is unnecessary to specify the
`source or destination of functional-type messages . Reception becomes the exclusive responsi(cid:173)
`bility of the receiving node. Figure 26.1 (2) also illustrates header bytes, which are primarily
`used for physical-type messages, and has two bytes : the first is the ID and the second is the tar(cid:173)
`get address .
`
`ID
`
`I- Data 1
`
`1. Header
`
`ID
`
`2. Header
`
`Message
`for Functional
`Data 1 I
`I Target
`for Physical Message Frames
`
`Frames
`
`FIGURE 26.1 Single-byte header protocol.
`
`The single-network architecture is usually associated with the multiple-byte header proto(cid:173)
`col, shown in Fig. 26.2. The first byte of the frame defines the priority and message types, func(cid:173)
`tional or physical.
`
`I Priority/Type
`
`Target
`
`Source
`
`Data 1
`
`FIGURE 26.2 Multiple-byte header protocol.
`
`Architecture Selection. Consideration must be given by the network designer as to whether
`a single-network architecture or a multiple-network architecture is preferable for an applica(cid:173)
`tion . For example, a multiple-network architecture could be based on one network optimized
`around data communication (Class B) protocol requirements , and another network opti(cid:173)
`mized around sensor type (Class A) multiplexing requirements . The Class B network may be
`characterized such that low latency is a significant requirement of the protocol and where the
`short functional type of messages can most effectively be used. A Class A network could han (cid:173)
`dle the vehicle's event -driven multiplexing requirements. See the next section on Class A net(cid:173)
`working for more information on Class A multiplexing considerations.
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`MULTIPLEX WIRING SYSTEMS
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`26.3
`
`Without regard to either the header or architecture selection , in Class B communicati ons
`the network consists of the interconnection of intelligent nodes such as an engine controller ,
`a body computer, a vehicle instrument cluster, and other modules. Such a network normally
`does not significantly reduce the base vehicle wiring but provides an intermodule data com(cid:173)
`munications capability for distributed processing. The data shared between modules may be
`repetitive in nature and sometimes requires handshaking between modules or acknowledg(cid:173)
`ment of data reception. As a result of handling the repetitive data and response-type data , a
`network can be optimized around functional addressing. Functional addressing sends data on
`the network, which can be received by one or more nodes without regard to the physical loca(cid:173)
`tion of the module but only by their "interest" in those specific functions . In general, the trans(cid:173)
`mitting node does not care which, if any, nodes receive the data it is sending. When physical
`addressing is required in a data communications network (Class B) , it is usually for vehicle
`maintenance purposes and can be easily handled without reducing netw ork bandwidth.
`The nature of Class A multiplexing requires the interconnection of limited intelligence
`nodes, often simply sensors or actuators. These Class A networks can significantly reduce the
`base vehicle wiring as well as potentially remove redundant sensors from the vehicle. The data
`shared between nodes in this case are generally event -driven in nature . In most vehicles, the
`number of event -driven signals predominates, but they are only needed infrequently. The
`message to "turn headlamps on," for example , can be easily seen as event-dri ven. Because
`these messages are infrequent ( only sent once when the signal changes) they genera lly
`require acknowledgment, either within the same message or a separate handsh ake/response
`message.
`The single-network architecture carries both the Class A and Class B messages on one net(cid:173)
`work and the multiple-byte header has the advantage of having more bits available for use in
`assigning message identifiers, priorities, message types, etc. The characteristics of both time(cid:173)
`critical and event -driven messages must be accommodated on a message-by-me ssage basis. In
`general , this level of complexity will need the flexibility of the multiple-byte head er structure.
`It should be clear that both network architectures must be cost effective for the applicatio n
`and the specific nodes on each network.
`The multiple network architecture tends to separate the Class A messages from the Class
`B messages and optimize each network and node interface for the specific characteristics of
`each network class. The time-critical messages could be exchanged on one network , while the
`event-driven messages are sent on another. For example, the data communication (Class B)
`repetitive messages can be handled on one network and the sensor and control (Class A) mul(cid:173)
`tiplexing requirements on another network. This architecture requires both networks to work
`together to achieve the total vehicle network requirements. If information is need ed between
`the multiple networks, care must be exercised to meet the needs of each of the networks. This
`concept of multiple networks is not limited to two, but can be extended to several separate
`networks if desired.
`
`Class A Network. Class A multiplexing 3 is most appropriate for low-speed body wiring and
`control functions. The example most often used to illustrate the benefits of Class A multi(cid:173)
`plexing is the base exterior lighting circuit. However , this example is the hardest function to
`cost-justify. The base exterior lighting system is extremely simple and very low cost. A multi(cid:173)
`plex network applied to this lighting system could result in increased wiring complexity and
`cost. Data integrity in the lighting system can be a stringent requirement for Class A multi(cid:173)
`plexing; e.g., a single-bit error that results in headlights "off" when they should be "on." Ade(cid:173)
`quate data integrity in a Class A multiplex network is a constraint and bit-error checking may
`be required.
`In the future, the results could change if new features, such as low-current switching or
`lamp -outage warning, became a requirement or new lamp technology , such as smart bulbs,
`became a reality. In general, the addition of new features will play a major role as to when and
`how multiplexing will become a cost-effective solution.
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`26.4
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`SAFETY , CONVENIENCE , ENTERTAINMENT, AND OTHER SYSTEMS
`
`Other Driving Forces. The design of vehicles to minimize manufacturing complexity is a
`major force that will lead to architecture partitioning development. The properly developed
`multiplex architecture can be very effective in reducing the number of parts in the assembly
`plants and built-in testability can substantially reduce vehicle build test time.
`Example Class A Systems. To illustrate how a Class A multiplex network could be used
`to simplify the vehicle wiring situation, consider the vehicle theft alarm system shown in Fig.
`26.3. Although this example does not represent the epitome in theft alarm features, it does
`illustrate the nonmultiplexed condition. The horn actuator and the sensor switches are all
`wired directly to the theft alarm module. The module is then armed by activating the dash arm
`switch. The module can be disarmed by either the driver door key switch, passenger door key
`switch, or the trunk key switch. When the module is armed, the horn is sounded when the
`hood, door, or trunk is tampered with .
`
`DRIVER DOOR
`switch r-
`Door
`i--------,
`Key Switch
`LEFT REAR DOOR
`Door Switch !
`t'
`...
`
`Hood Switch
`
`Dash Arm
`Switch
`
`,-- -
`
`-----<r---f
`
`~ -
`
`--~
`
`PASSENGER DOOR
`.-i Door S~i tch
`Key switch
`...
`RIGHT REAR DOOR
`..
`9]. Door Switch
`1 Trunk
`+ Trunk Key switch
`
`switch
`
`Vehicle
`
`Theft
`Module
`
`FIGURE 26.3 Vehicle theft alarm system.
`
`Vehicle
`
`Horn
`
`Y Ground
`
`The vehicle theft alarm system shown in Fig. 26.4 illustrates a near-optimal configuration
`of a Class A network. The sensors and actuators are integrated with the multiplexing elec(cid:173)
`tronics so that they can communicate over a single wire to the theft alarm module. The inte(cid:173)
`gration of electronics into t