1、Multiplex Communication Serial Data Networking Applied to Vehicular Engineering Christopher Albert LupiniVehicle Multiplex Communication Serial Data Networking Applied to Vehicular EngineeringOther SAE titles of interest: IDB-C Data Bus: Report on Studies for Modeling, Simulation, and Signal Analysi
2、s; and EMC/EMI Measurements and Testing by Daniel J. Guzman (Order No. RR-014) In-Vehicle Networks, Safety Critical Systems, Accelerated Testing, and Reliability (Order No. SP-1783) Software/Hardware and Systems Engineering (Order No. SP-1781) For more information or to order a book, contact SAE at
3、400 Commonwealth Drive, Warrendale, PA 15096-0001; phone (724) 776-4970; fax (724) 776-0790; e-mail CustomerServicesae.org; website http:/store.sae.org.Vehicle Multiplex Communication Serial Data Networking Applied to Vehicular Engineering Christopher Albert Lupini Warrendale, Pa. Copyright 2004 SAE
4、 International eISBN: 978-0-7680-5208-4All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. For permis
5、sion and licensing requests, contact: SAE Permissions 400 Commonwealth Drive Warrendale, PA 15096-0001 USA E-mail: permissionssae.org Tel: 724-772-4028 Fax: 724-772-4891 Library of Congress Cataloging-in-Publication Data Lupini, Christopher Albert. Vehicle multiplex communication : serial data netwo
6、rking applied to vehicular engineering / Christopher Albert Lupini. p. cm. Includes bibliographical references and index. ISBN 0-7680-1218-X 1. AutomobilesElectronic equipmentComputer networks. 2. Automotive computers. 3. Computer interfaces. 4. Data communication systems. 5. Multiplexing. I. Title.
7、 TL272.53.L87 2004 629.273dc22 2004042962 SAE 400 Commonwealth Drive Warrendale, PA 15096-0001 USA E-mail: CustomerServicesae.org Tel: 877-606-7323 (inside USA and Canada) 724-776-4970 (outside USA) Fax: 724-776-1615 Copyright 2004 SAE International ISBN 0-7680-1218-X SAE Order No. R-340 Printed in
8、the United States of America.Acknowledgments The author thanks Delphi Electronics and Safety for assisting him in writing this book. Appreciation is also given to the many reviewers of the manuscript, especially Matt Ruff, Nigel Allison, and Tim Thomas. Also, a special thank you to my wife Carrie fo
9、r her unlimited support during this long process. vTable of Contents Chapter 1 Introduction 1 Chapter 2 Historical Perspective 5 Chapter 3 Background 11 Chapter 4 Onboard Diagnostics (OBD) 33 Chapter 5 Encoding 43 Chapter 6 Error Handling 61 Chapter 7 Media Characteristics 73 Chapter 8 The Vehicle L
10、evel 83 Chapter 9 The Electronic Control Unit (ECU) Level 95 Chapter 10 The Integrated Circuit (IC) Level 115 Chapter 11 Electromagnetic Compatibility (EMC) 145 Chapter 12 What Is a Standard? 155 Chapter 13 Class A Protocols 165 Chapter 14 Class B Protocols 179 Chapter 15 Class C Protocols 199 Chapt
11、er 16 Diagnostic Protocols, Airbag Protocols, X-by-Wire Protocols, Mobile Multimedia Protocols, and Wireless Protocols 221 Chapter 17 Data Link Usage . 233 Chapter 18 Manufacturing Automation 253 viiVehicle Multiplex Communication Chapter 19 Industry Activities 259 Chapter 20 Future Trends 271 Appen
12、dix A Glossary of Terms 283 Appendix B List of Acronyms 299 Appendix C Bus Comparison Tables 305 Appendix D List of SAE and ISO Committees 315 Index 317 About the Author 383 viiiChapter 1 Introduction Overview This text is an introductory overview of vehicle multiplexing. The intended audience is en
13、gineers and managers working in the field of automotive and other vehicular electronics. The content for this book was developed from a three-day class on in-vehicle networking that has been taught in the public sector since 1993. A series of classes covering this material, and much more, are availa
14、ble now through Dearborn Group Technology, Inc. (). Multiplexing, or in-vehicle networking, is one of the most popular areas of vehicle electronics currently. All vehicle original equipment manufacturers (OEMs), electronic control unit (ECU) suppliers, and integrated circuit (IC) vendors to the auto
15、motive industry are working on multiplex products. Multiplexing is the technology of applying serial data communications to the electric/electronic functions of a vehicle. Multiplexing can be best discussed at three levels: the vehicle level, the ECU or component level, and the IC level. Within each
16、 level are partitions for software and hardware, and within each partition are divisions of functionality such as buffer size. The following chapters will help the reader to acquire a basic understanding of vehicle multiplexing systems primarily from the viewpoint of the passenger car and light truc
17、k. Some discussion of heavy-duty and off-road vehicle multi- plexing will be presented, as will be a look at industrial automationa fast- growing multiplex field already eclipsing automotive usage. Hereafter, “automotive“ will be used interchangeably with “vehicle.“ Hardware and software issues will
18、 be presented for the more common proto- cols available. This survey should enable the reader to understand how 1Vehicle Multiplex Communication multiplexing is generally done, so new protocols should present no difficulty as they arise. Much like software languages, all multiplex protocols have man
19、y things in common, and new schemes are simple to learn, once one or more are mastered. Although this is an introductory and background text, information is presented on important technical issues such as electromagnetic compatibility (EMC). Within this realm, problems with electrostatic discharge (
20、ESD), radiated emis- sions, and radiated immunity are important topics. It is assumed that the reader has education and/or experience in electrical engineering. Some background in microcomputer operation and program- ming is also helpful. Basic techniques of binary/hexadecimal data conversion and co
21、mputer architectures will not be presented. The Contents of the Book The remainder of this book includes the following chapters: Historical Perspective How and why did multiplexing come about in the first place? Background Terms and definitions needed to discuss multiplexing Onboard Diagnostics (OBD
22、) What is it? Encoding Pros/cons of various encoding techniques Error Handling How to protect from disruptive transients? 2Introduction Media Characteristics What do we actually use to connect the nodes? The Vehicle Level A look at multiplexing in general from the viewpoint of the vehicle The Electr
23、onic Control Unit (ECU) Level A look at multiplexing in general from the viewpoint of the component The IC Level A look at multiplexing in general from the viewpoint of the IC Electromagnetic Compatibility How does the multiplex system interact with the outside world? What Is a Standard? Introduces
24、the world governing bodies for standards Class A Protocols The low-speed protocols Class B Protocols The medium-speed protocols Class C Protocols The high-speed protocols Diagnostic Protocols, Airbag Protocols, X-by-Wire Protocols, Mobile Multi- media Protocols, and Wireless Protocols 3Vehicle Multi
25、plex Communication Data Link Usage Protocol comparison chart Company-by-company look at who is using what Manufacturing Automation Industrial usage of multiplexing Industry Activities What are General Motors (GM), Ford, and Daimler Chrysler doing together? Status of any worldwide consortia Future Tr
26、ends Whats next? Two appendices are included that give common terminology (glossary) and acronyms used in this book. The last two appendices are a survey of some of the known automotive (or related) protocols and a list of relevant Interna- tional Organization for Standardization (ISO) and Society o
27、f Automotive Engineers (SAE) committees. 4Chapter 2 Historical Perspective Introduction Multiplexing development has been in vogue since the mid-1970s. Initially, it was seen as a way to ease the diagnosis of electrical functions in vehicles 1. Multiplex usage in military applications (i.e., MIL-STD
28、-1553) was already well established at that time. The surge of computing power primarily due to the emissions requirements of the late 1970s and early 1980s created renewed interest in multiplexing and in-vehicle networks. By the mid-1980s, most vehicle manufacturers had at least one serial data lin
29、k protocol in production. The 1990s were supposed to be the “boom“ years for multiplexing. Unfortu- nately, leveling-off of electronic content and cost restraints put a serious damper on new applications, and this boom has turned into a “fast burn.“ The Multiplexing Paradox The multiplexing paradox
30、involves the apparent contradiction between the popularity of multiplexing and actual usage of the technology. Although it is a powerful automotive systems architectural tool, it has not gained the wide- spread usage once predicted. These are some of the reasons that multiplexing has not caught on a
31、s it should have: 1. It is not cost-effective. This is true in many cases because the cost comparison has looked simply at removing several wires and connectors and replacing them with 5Vehicle Multiplex Communication additional protocol handling circuitry. This is not a fair analysis because it ove
32、rlooks the cost savings of easier problem diagnosis, simpler servicing, better future expandability, easier removal/addition of vehicle options, and more choices for function partitioning and distribution among the ECUs. It is still, however, the most powerful argument against multiplexing. Unfortun
33、ately, saving a penny today is considered more worthwhile than saving a dollar several years down the road. 2. It breeds competition. Believe it or not, multiplexing is considered a threat to ECU suppliers because it opens the door to more competition to supply components with a common serial data l
34、ink interface such as the controller area network (CAN). This is mostly in the U.S. industry. Europes vehicle OEMs are almost entirely dependent on outside ECU suppliers, and these suppliers have always had a lot of competition. 3. Little or no perceived customer benefit. Customer means the vehicle
35、consumer. “Multiplexing“ is not listed as content on the vehicle window sticker. How can one make the vehicle consumer realize the difference between a car with multiplexing and one without? The key technical point is that almost anything multiplexing is doing could have been accomplished with discr
36、ete wires (if space were available). These are some of the positive reasons cited for using multiplexing: 1. Decreases the size of wiring harnesses Multiplexing signals can definitely reduce the number of interconnecting wires in the vehicle and save weight and space. Where this has the most effect
37、is in constrained areas such as door pillars and underhood. 2. Economies of scale With a standard multiplex protocol, there should be a reduced piece cost of the hardware (i.e., ICs) that is included in the nodes. The theory says 6Historical Perspective there will be a large demand for chips to impl
38、ement the common interface(s), and therefore, prices will fall. We are witnessing this today with CAN. 3. Sharing of parametric data This item has already been proven in production. Redundant sensors, such as those for vehicle speed, can be eliminated because one sensor can supply its parametric inf
39、ormation across the network for use by mul- tiple nodes. 4. Increased reliability and test Multiplexing ECUs should allow better diagnosing of their circuitry because they can transmit and receive data from any node via one access port, that is, the data link controller (DLC). A built-in test can be
40、 designed in because the nodes may communicate with each other and check each others functions upon initialization. Including the benefit of number (3) above, the hope is that low-cost vehicle electronic diagnostic tools will become available to the general public. The dream is for a $99 handheld sc
41、anner so that shade-tree mechanics may troubleshoot their vehicles. Now, some government entities may not like this because of the possibility of tampering with emission control func- tions, but most vehicle consumers would welcome a cheap tool. A powerful topic relating to diagnosis and test is the
42、 idea of having a flight recorder, or “black box,“ as part of the vehicles electronics 2. As with aircraft, this boxs contents could help in recreating a crash. IEEE 1616 is an attempt to standardize this. More benignly, it could also be used to troubleshoot malfunctionsespecially those that do not
43、occur with a tech- nician at the wheel. 5. Greater flexibility in vehicle content If the rule of open architecture is followed (see Chapter 3), multiplexing should greatly help the problem of creating “world cars“ and other kinds 7Vehicle Multiplex Communication of flexible platforms. Vehicle option
44、s could be added more easily during assembly, or even at the dealershipsometimes months or years after the original sale. 6. Lower assembly and installation costs This is an area that must be considered when comparing the cost/benefits of multiplexing to discrete wiring. Multiplexing should make it
45、easier to design, assemble, and maintain the vehicle. 7. Adding the impossible function Finally, many people believe that probably the most important enabler for multiplexing is that it can help to include a feature or function that other- wise would not have been part of the vehicle. Examples of th
46、is are the flight recorder, a built-in test among the ECUs, a $99 scan tool, the mobile office, and so forth. An Early Multiplex Design Figure 2.1 illustrates one of the first multiplexed networks to be found in a production vehicle 3. Note that this design also illustrates the common occurrence of
47、multiple networks. The 160 b/s connection was strictly for off- board diagnosis. The 8192 b/s link was the universal asynchronous receiver/ transmitter (UART) bus that connected three ECUs to the assembly line connector. A 1 kb/s Entertainment & Comfort (E&C) bus connected the cathode ray tube (CRT)
48、 controller to the remote radio chassis. Vehicle Multiplex Comparison to Industry Compared to other (nonautomotive) schemes, in-vehicle networking is rather slow and suitable only for short distances (Fig. 2.2). Automotive needs, how- ever, are much more demanding than most other uses. The in-car en
49、viron- ment is harsh with respect to temperature, vibration, and electrical noise, not to mention that cost has to be low in a business where pennies count. 8Historical Perspective Fig. 2.1 Early multiplex implementation. Fig. 2.2 Multiplex performance comparison. 9Vehicle Multiplex Communication As an example of the extent to which serial data links have been already used in automobiles, GM has used the following in production (sometimes several in the same vehicle): 160 bps diagnostic bit stream 1980 8192 bps
