®
J1939-21
REV.
DEC2006
SURFACE
VEHICLE
RECOMMENDED
PRACTICE
Issued 1994-07
Revised 2006-12
Superseding J1939-21 APR2001
Data Link Layer
RATIONALE
This SAE Recommended Practice revision incorporates changes to the assigned SAE Reserved Bit to be the Extended
Data Page Bit, Acknowledgement sections, the new proprietary A2 PGN (PGN 126720) and includes new SPN
assignments in Appendix D.
The 'Reserved' bit of the 29-bit of J1939 header has been defined as the 'Extended Data Page' (EDP) bit. The J1939
Subcommittee has concerns there might be existing and developing components for J1939 that don't verify the
Reserved/EDP bit is zero (0) before processing the 29-bit header per the J1939-21 structure. It is important that existing
and future J1939 applications examine the values of the EDP and DP bits before interpreting the remaining 24 bits per the
PDU Format (PF), PDU Specific (PS), and Source Address (SA) structure specified in J1939-21.
Backward compatibility is maintained during this change by specifying the Extended Data Page bit value of zero for all
existing J1939 PGNs. Prior to this functional change, J1939-21 required the Reserved bit to be set to zero (0) in all J1939
PGN Data Frame headers.
FOREWORD
This series of SAE Recommended Practices have been developed by the Truck and Bus Control and Communications
Network Subcommittee of the Truck and Bus Electrical and Electronics Committee. The objectives of the subcommittee
are to develop information reports, recommended practices, and standards concerned with the requirements, design, and
usage of devices that transmit electronic signals and control information among vehicle components. The usage of these
Recommended Practices is not limited to truck and bus applications; other applications may be accommodated with
immediate support being provided for construction and agricultural equipment, and stationary power systems.
These SAE Recommended Practices are intended as a guide toward standard practice and are subject to change so as
to keep pace with experience and technical advances.
This data link layer is used for all SAE J1939 applications. It is the characteristic that is common across all SAE J1939
applications.
__________________________________________________________________________________________________________________________________________
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 therefrom, 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 © 2006 SAE International
All 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.
TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada)
Tel: 724-776-4970 (outside USA)
Fax: 724-776-0790
Email: CustomerService@SAE.org
SAE WEB ADDRESS: http://www.SAE.org
Copyright SAE International
Provided by IHS under license with SAE
Not for Resale
No reproduction or networking permitted without license from IHS
--`,,```,,,,````-`-`,,`,,`,`,,`---
SAE J1939-21 Revised December 2006
Page 2 of 47
TABLE OF CONTENTS
1.
Scope ............................................................................................................................................................ 4
2. References.................................................................................................................................................... 4
2.1 Applicable Publications ................................................................................................................................. 4
2.1.1 SAE Publications........................................................................................................................................... 4
2.2 Related Publications ..................................................................................................................................... 4
2.2.1 ISO Publications............................................................................................................................................ 4
3. Definitions ..................................................................................................................................................... 4
4. Abbreviations(R) ........................................................................................................................................... 4
5. Technical Requirements ............................................................................................................................... 5
5.1 Message/Frame Format................................................................................................................................ 5
5.1.1 SAE J1939 Message Frame Format (“CAN 2.0B” Extended Frame Format) (R) ........................................ 6
5.1.2 Parameter Group Number (PGN) ................................................................................................................. 6
5.1.3 SAE J1939 Support of “CAN 2.0B” Standard Frame Format Messages.................................................... 10
5.2 Protocol Data Unit (PDU)............................................................................................................................ 11
5.2.1 Priority (P) ................................................................................................................................................... 11
5.2.2 Extended Data Page (EDP) (R).................................................................................................................. 11
5.2.3 Data Page (DP) (R)..................................................................................................................................... 11
5.2.4 PDU Format (PF) ........................................................................................................................................ 14
5.2.5 PDU Specific (PS)....................................................................................................................................... 14
5.2.5.1 Destination Address (DA) ........................................................................................................................... 14
5.2.5.2 Group Extension (GE)................................................................................................................................. 14
5.2.6 Source Address (SA) .................................................................................................................................. 14
5.2.7 Data Field.................................................................................................................................................... 15
5.2.7.1 Data from 0 to 8 Bytes ................................................................................................................................ 15
5.2.7.2 Data from 9 Up to 1785 Bytes..................................................................................................................... 15
5.3 Protocol Data Unit (PDU) Formats ............................................................................................................. 15
5.3.1 PDU1 Format (R) ............................................................................................................................. 16
5.3.2 PDU2 Format(R) ......................................................................................................................................... 17
5.4 Message Types........................................................................................................................................... 18
5.4.1 Command.................................................................................................................................................... 18
5.4.2 Request....................................................................................................................................................... 18
5.4.3 Broadcast/Response................................................................................................................................... 21
5.4.4 Acknowledgment (R)......................................................................................................................... 21
5.4.5 Group Function ........................................................................................................................................... 23
5.4.6 Request2..................................................................................................................................................... 25
5.4.7 Transfer....................................................................................................................................................... 26
5.5 Message Priority ......................................................................................................................................... 27
5.6 Bus Access ................................................................................................................................................. 28
5.7 Contention-Based Arbitration...................................................................................................................... 28
5.8 Error Detection............................................................................................................................................ 28
5.9 Assignment Process for Source Addresses and Parameter Group Numbers ........................................... 28
5.9.1 Address Assignment Criteria ...................................................................................................................... 28
5.9.2 Parameter Group Assignment Criteria........................................................................................................ 29
5.9.3 Data Field Definition.................................................................................................................................... 30
5.10 Transport Protocol Functions...................................................................................................................... 30
5.10.1 Packetization and Reassembly................................................................................................................... 30
5.10.1.1 Message Packets........................................................................................................................................ 30
5.10.1.2 Sequence Numbers .................................................................................................................................... 30
5.10.1.3 Packetization............................................................................................................................................... 30
5.10.1.4 Reassembly ................................................................................................................................................ 31
5.10.2 Connection Management............................................................................................................................ 31
5.10.2.1 Multipacket Broadcast................................................................................................................................. 31
5.10.2.2 Connection Initiation ................................................................................................................................... 31
5.10.2.3 Data Transfer .............................................................................................................................................. 31
Copyright SAE International
Provided by IHS under license with SAE
Not for Resale
No reproduction or networking permitted without license from IHS
--`,,```,,,,````-`-`,,`,,`,`,,`---
SAE J1939-21 Revised December 2006
Page 3 of 47
5.10.2.4
Connection Closure .................................................................................................................................... 32
5.10.3 Transport Protocol—Connection Management Messages......................................................................... 33
5.10.3.1 Connection Mode Request to Send (TP.CM_RTS)....................................................................................34
5.10.3.2 Connection Mode Clear to Send (TP.CM_CTS)......................................................................................... 35
5.10.3.3 End of Message Acknowledgment (TP.CM_EndOfMsgACK) .................................................................... 35
5.10.3.4 Connection Abort (TP.Conn_Abort)............................................................................................................ 35
5.10.3.5 Broadcast Announce Message (BAM)........................................................................................................ 36
5.10.4 Transport Protocol—Data Transfer Message (TP.DT)............................................................................... 36
5.10.5 Connection Constraints............................................................................................................................... 37
5.10.5.1 Number and Type of Connections a Node Must Support........................................................................... 37
5.10.5.2 Intended Transport Protocol Use................................................................................................................ 37
5.10.5.3 Concurrent PGN Reception ........................................................................................................................ 37
5.11 PDU Processing Requirements .................................................................................................................. 37
5.12 Application Notes ........................................................................................................................................ 38
5.12.1 High Data Rates.......................................................................................................................................... 38
5.12.2 Request Scheduling.................................................................................................................................... 38
5.12.3 Device Response Time and Timeout Defaults ........................................................................................... 38
5.12.4 Required Responses .................................................................................................................................. 38
5.12.5 Transmission of PGNs to Specific or Global Destinations.......................................................................... 38
5.12.6 CTS Number of Packet Recommendation.................................................................................................. 39
6. Notes........................................................................................................................................................... 39
6.1 Marginal Indicia........................................................................................................................................... 39
APPENDIX A SAE J1939 PDU Processing⎯Typical Receive Routine .............................................................................. 40
APPENDIX B Communication Message Types................................................................................................................... 41
APPENDIX C Transport Protocol Transfer Sequences....................................................................................................... 42
APPENDIX D Assignments of SPNs for J1939-21.............................................................................................................. 47
LIST OF FIGURES
Figure 1 CAN Data Frames(R) ..............................................................................................................................................7
Figure 2 Application of OSI Model by SAE J1939(R) ............................................................................................................8
Figure 3 Protocol Data Unit(R).............................................................................................................................................11
Figure 4 SAE J1939 Parameter Group Number Template(R).............................................................................................13
Figure 5 Available PDU Formats(R) ....................................................................................................................................16
Figure 6 PDU1 Format (R)..................................................................................................................................................17
Figure 7 PDU2 Format(R)....................................................................................................................................................18
Figure 8 Request PGN Definition (R)...................................................................................................................................19
Figure 9 Acknowledgment PGN Definition (R) ....................................................................................................................23
Figure 10 Proprietary A PGN Definition (R).........................................................................................................................24
Figure 11 Proprietary A2 PGN definition (R) .......................................................................................................................25
Figure 12 Proprietary B PGN Definition (R).........................................................................................................................25
Figure 13 Request2 PGN Format (R) ..................................................................................................................................26
Figure 14 Transfer PGN Format (R) ....................................................................................................................................27
Figure 15 Format of Messages for Transport Protocol (R).................................................................................................33
Figure 16 Transport Protocol—Data Transfer Message (TP.DT) (R)..................................................................................36
Figure A1 Typical Receive Routine......................................................................................................................................40
Figure B1 Example of Communication Message Types (R)................................................................................................41
Figure C1 Data Transfer without Errors...............................................................................................................................42
Figure C2 Data Transfer with Errors....................................................................................................................................43
Figure C3 Broadcast Data Transfer.....................................................................................................................................44
Figure C4 Data Transfer Utilizing RTS Maximum Number of Packets Capability...............................................................45
Figure C5 Data Transfer Not Able to Utilize RTS Maximum Number of Packets Capability...............................................46
LIST OF TABLES
Table 1 Mapping of SAE J1939 into CAN’s Arbitration and Control Fields(R)......................................................................9
Table 2 Parameter Group Number Examples (SAE use EDP=0) (R) ................................................................................10
Table 3 Definition of Extended Data Page and Data Page Use(R).....................................................................................12
Table 4 PDU Specific...........................................................................................................................................................14
Copyright SAE International
Provided by IHS under license with SAE
Not for Resale
No reproduction or networking permitted without license from IHS
--`,,```,,,,````-`-`,,`,,`,`,,`---
SAE J1939-21 Revised December 2006
Page 4 of 47
Table 5 PDU1 and PDU2 Transmit, Request and Response Requirements ......................................................................19
Table 6 Use of the Specified Fields in SAE J1939 PDU1 Format.......................................................................................20
Table 7 Connection Abort Reason (R).................................................................................................................................36
Table D1 J1939-21 SPN Usage (R)....................................................................................................................................47
1. SCOPE
The SAE J1939 documents are intended for light, medium, and heavy-duty vehicles used on or off road as well as
appropriate stationary applications which use vehicle derived components (e.g. generator sets). Vehicles of interest
include, but are not limited to, on- and off-highway trucks and their trailers, construction equipment, and agricultural
equipment and implements.
The purpose of these documents is to provide an open interconnect system for electronic systems. It is the intention of
these documents to allow Electronic Control Units to communicate with each other by providing a standard architecture.
This particular document, SAE J1939-21, describes the data link layer using the CAN protocol with 29-bit Identifiers. For
SAE J1939 no alternative data link layers are permitted.
2. REFERENCES
2.1 Applicable Publications
General information regarding this series of recommended practices is found in SAE J1939. The latest issue of SAE
publications shall apply.
2.1.1 SAE Publications
Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001. Tel: 877 606-7323 (inside USA and
Canada) or 724 776 4970 (Outside USA), www.sae.org. Unless otherwise specified, the latest publication shall apply..
SAE J1939 Recommended Practice for a Serial Control and Communications Vehicle Network is the parent
document and should be referenced in general.
SAE J1939-71 Vehicle Application Layer
SAE J1939-81 Network Management
2.2 Related Publications
The following publications are provided for information purposes only and are not a required part of this document.
2.2.1 ISO Publications
Available from ANSI, 25 West 43
rd
Street, New York, NY 10036-8002, Tel: 212-642-4900, www.ansi.org.
ISO 11898 (Amended) Road Vehicles—Interchange of digital information—Controller area network (CAN) for high-speed
communications AMENDMENT 1
ISO 15765-3 Road Vehicles—Diagnostics on Controller Area Network (CAN)—Part 3; Implementation of Unified
Diagnostic Services (UDS on CAN), October 23, 2003
3. DEFINITIONS
Terms and definitions are defined in SAE J1939.
4. ABBREVIATIONS(R)
ACK Acknowledgment
BAM Broadcast Announce Message
Copyright SAE International
Provided by IHS under license with SAE
Not for Resale
No reproduction or networking permitted without license from IHS
--`,,```,,,,````-`-`,,`,,`,`,,`---
SAE J1939-21 Revised December 2006
Page 5 of 47
CAN Controller Area Network
CRC Cyclic Redundancy Check
CTS Clear-to-Send
DA Destination Address
DLC Data Length Code
DP Data Page
DT Data Transfer
EDP Extended Data Page
EOF End of Frame
GE Group Extension
ID Identifier
IDE Identifier Extension Bit
LLC Logical Link Control
LSB Least Significant Byte or Least Significant Bit
MAC Medium Access Control
MF Manufacturer
MSB Most Significant Byte or Most Significant Bit
NA Not Allowed
NACK Negative-Acknowledgment
P Priority
PDU Protocol Data Unit
PF PDU Format
PGN Parameter Group Number
PS PDU Specific
RTR Remote Transmission Request
RTS Request-to-Send
SA Source Address
SOF Start of Frame
SPN Suspect Parameter Number
SRR Substitute Remote Request
TP Transport Protocol
T
h
Hold Time
T
r
Response Time
un Undefined
5. TECHNICAL REQUIREMENTS
The data link layer provides for the reliable transfer of data across the physical link. This consists of sending the CAN
Data Frame with the necessary synchronization, sequence control, error control, and flow control. The flow control is
accomplished by a consistent message/frame format.
5.1 Message/Frame Format
Message format conforms to the CAN requirements. The CAN specification referenced throughout this document is CAN
Specification 2.0 Part B, September 1991. It should be noted that when there are differences between the CAN
specification and SAE J1939, then SAE J1939 is the guiding document.
Copyright SAE International
Provided by IHS under license with SAE
Not for Resale
No reproduction or networking permitted without license from IHS
--`,,```,,,,````-`-`,,`,,`,`,,`---
