SAE-J1708-2008.pdf
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1、_ SAE Technical Standards Board Rules provide that: “ This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising ther
2、efrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2008 SAE International All rights reserved. No part of this publication
3、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. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA
4、) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org J1708 OCT2008 SURFACE VEHICLE RECOMMENDED PRACTICE Issued1986-01 Revised 2008-10 Superseding J1708 AUG2004 Serial Data Communications Between Microcomputer Systems in Heavy-Duty Vehicle Applications RATIONALE Change
5、 made to Section 6.3.3.2 to direct device manufacturers using MIDs less than 128 that interact with PLC applications to consult latest SAE J2497. FOREWORD The SAE group responsible for the content of this recommended practice was revised to the SAE Low Speed Communications Network Subcommittee spons
6、ored by the SAE Truck and Bus Electrical and Electronics Committee. This Document was revised to comply with the new SAE Technical Standards Board format. Earlier versions of this document stated: This SAE/TMC Joint Recommended Practice has been developed by the Truck and Bus Electronic Interface Su
7、bcommittee of the Truck and Bus Electrical Committee and by the S.1 Study Group of the Maintenance Council. The objectives of the subcommittee are to develop information reports, recommended practices, and standards concerned with the interface requirements and connecting devices required in the tra
8、nsmission of electronic signals and information among truck and bus components. Objectives: Some of the goals of the subcommittee in developing this document were to: a. Minimize hardware cost and overhead. b. Provide flexibility for expansion and technology advancements with minimum hardware and so
9、ftware impact on in- place assemblies. c. Utilize widely accepted electronics industry standard hardware and protocol to give designers flexibility in parts selection. d. Provide a high degree of electromagnetic compatibility. e. Provide original equipment manufacturers, suppliers, and aftermarket s
10、uppliers the flexibility to customize for product individuality and for proprietary considerations. -,-,- SAE J1708 Revised OCT2008 - 2 - TABLE OF CONTENTS 1.SCOPE3 1.1Purpose.3 2.REFERENCES3 2.1Applicable Publications.3 2.1.1SAE Publications.3 2.1.2EIA Publication3 3.DEFINITIONS .4 3.1Bus Access Ti
11、me 4 3.2Baud4 3.3Bit Time.4 3.4Character 4 3.5Character Time .4 3.6Contention.4 3.7Differential Signal4 3.8Idle State.4 3.9Idle Line.4 3.10Message Priority .4 3.11Node4 3.12Start Bit5 3.13Stop Bit5 4.ELECTRICAL PARAMETERS5 4.1Logic State5 4.2Bus State.5 4.2.1Logic High State5 4.2.2Logic Low State.5
12、4.3Network Capacity5 4.4Bus Termination5 4.5Ground 5 4.6Wire.6 4.7Length .6 5.NETWORK PARAMETERS6 5.1Network Topology.6 5.2Network Access 6 5.2.1Idle Line - Bus Synchronization by a Receiver.6 5.2.2Bus Access .7 5.2.3Bus Contention9 6.PROTOCOL9 6.1Bit Time.9 6.2Character Format9 6.3Message Format.9
13、6.3.1Message Content9 6.3.2Inter-Character Bit Time10 6.3.3Message Identification Character (MID).10 6.3.4Data Characters11 6.3.5Checksum.11 6.3.6Message Length12 6.3.7Message Length Exceptions.12 7.NOTES12 7.1Marginal Indicia.12 SAE J1708 Revised OCT2008 - 3 - APPENDIX A SERIAL DATA BUS STANDARD NO
14、DE (UNIPOLAR DRIVE WITH PASSIVE TERMINATION IN EACH MODULE)13 APPENDIX B EXAMPLE BUS REACCESS PROCEDURE14 1. SCOPE This SAE Recommended Practice defines a recommended practice for implementing a bidirectional, serial communication link among modules containing microcomputers. This document defines t
15、hose parameters of the serial link that relate primarily to hardware and basic software compatibility such as interface requirements, system protocol, and message format. The actual data to be transmitted by particular modules, which is an important aspect of communications compatibility, is not spe
16、cified in this document. These and other details of communication link implementation and use should be specified in the separate application documents referenced in Section 2. 1.1 Purpose The purpose of this document is to define a general-purpose serial data communication link that may be utilized
17、 in heavy- duty vehicle applications. It is intended to serve as a guide toward standard practice to promote serial communication compatibility among microcomputer-based modules. The primary use of the general-purpose communications link is expected to be the sharing of data among stand-alone module
18、s to cost effectively enhance their operation. Communication links used to implement functions that require a dedicated communication link between specific modules may deviate from this document. 2. REFERENCES 2.1 Applicable Publications The following publications form a part of the specification to
19、 the extent specified herein. Unless otherwise indicated the latest revision of SAE publications shall apply. It is recommended that a separate applications document be published by the manufacturer for each device using the serial link. These documents should define the data format, message I.D.s,
20、message priorities, error detection (and correction), maximum message length, percent bus utilization, and methods of physically adding/removing units to/from the line for the particular application. 2.1.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 1509
21、6-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. SAE J1455 Recommended Environmental Practices for Electronic Equipment Design in Heavy-Duty Vehicle Applications SAE J1587 Electronic Data Interchange Between Microcomputer Systems in Heavy-Duty Vehicle App
22、lications SAE J1922 Powertrain Control Interface for Electronic Controls Used in Medium- and Heavy-Duty Diesel On-Highway Vehicle Applications SAE J2497 Power Line Carrier Communications for Commercial Vehicles 2.1.2 EIA Publication Available from Electronic Industries Alliance, 2500 Wilson Boulevar
23、d, Arlington, VA 22201-3834, Tel: 703-907-7500, www.eia.org. EIA RS-485 Standard for Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems, April 1983 -,-,- SAE J1708 Revised OCT2008 - 4 - 3. DEFINITIONS 3.1 Bus Access Time A time duration equal to the
24、 minimum time of an Idle Line plus the product of 2 bit times and the message priority (which ranges from 1 to 8). An example is shown in 5.2.2.3. 3.2 Baud The maximum number of analog signal transitions per second that can occur on a channel. In this coding system, this is the reciprocal of the bit
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