Quo vadis SAE J1939 standardization

Peter Fellmeth, Holger Söhnle (Vector Informatik)

Standardization

has forced commercial ve- hicle developers to work at the limits of performance [2]. From a communication perspective, development of the 500-kbit/s data trans- port layer is a long overdue step. European commercial vehicle producers in partic- ular are seeking a final de- cision in the near future. The specification will be re- leased in a separate docu- ment, J1939-14, and its key aspects are: ue to new application erates by the plug-and-play chased either individually X Twice the bit-rate, Dlayer requirements, principle. The J1939 stan- or together as a package in 500 kbit/s instead of SAE is continuing to de- dard is an active standard so-called “JPaks” from the 250 kbit/s velop the J1939 standard, that currently consists of SAE website [1]. X Use of shielded and un- which is primarily used 19 documents. The respon- shielded cable as de- to network powertrains in sible SAE subcommittees fined in [2] and [3] is still commercial vehicles. How- generally meet four times a More bandwidth possible ever, optimizations and ex- year to decide on changes X Topology is essentially a tensions are being made and further developments. For years now, the maxi- bus that has branch lines in the other communication The current versions of the mum 250-kbit/s bandwidth with a max. length of 1 m. layers as well, right up to the documents may be pur- specified in the standard To connect diagnostic physical transmission layer. This article summarizes the current state of discussions within the SAE J1939 work- ing committee, such as the planned introduction of the 500-kbit/s physical trans- mission layer and chang- es to network management. Moreover, it also explains ongoing efforts to standard- ize J1939 in Autosar Re- lease 4 and WWH-OBD (world-wide harmonized on- board diagnostics) diagnos- tics. Based on the CAN bus (high-speed CAN per ISO 11898), the SAE J1939 standard is used primarily to network the powertrain and chassis in commercial vehicles. The protocol cre- ates a uniform foundation for communication between the electronic ECUs (elec- tronic control unit) and op- Status of SAE J1939 documents (September 2010)

62 CAN Newsletter 1/2011 Microcontrollers Digital Signal Analog Memory RF & Wireless Controllers tools, a branch line (from of sensors with a direct bus the diagnostic socket connection. The number of to the diagnostic tool) new devices is growing rap- with a length of 5 m may idly due to heightened ex- sometimes be used. haust emissions require- X The bus is terminated at ments and the addition of both ends with a char- assistance systems. Many acteristic impedance of alternatives were proposed 120 Ÿ. Up to 30 nodes but then rejected. They are possible. ranged from a dedicated network for sensors to im- Standardization The specification for the di- plementation of a new pro- agnostic plug [4] was adapt- tocol – e.g. by using previ- ed to 500-kbit/s operation. ously reserved data pages. In addition, a new “Type II” Meanwhile, the fact diagnostic socket is being was that SAE has not as- used in the vehicle, which signed any more new ad- has a green color-coding, dresses. That was an un- and its connector keying satisfactory situation for prevents use of the previous ECU suppliers. Often, they 250-kbit/s “Type I” diagnos- did not know whether their tic plug. A “Type II” plug is product designs would have compatible with a “Type I” lasting value. In the latest Fig. 2: Layout of a 29-bit CAN-ID in J1939 networks socket. Another change is version of Network Manage- that the “Type II” diagnos- ment, SAE recommends im- specific components of the These changes in tic socket defines pins pre- plementing “Address Arbi- 64-bit device name. This Network Management are viously used for SAE J1708/ trary Capable” ECUs. These might be necessary if the supported in version 7.5 J1587 as reserved. Conse- ECUs are able to compute relevant function or mea- of Vector’s CANalyzer. quently, a J1708-/J1587-net- their own addresses based surement parameter is de- J1939 analysis tool and its work can no longer be ad- on the momentary vehicle rived from the device name. CA Noe. J1939 test tool. dressed via a “Type II” diag- configuration – and indeed So, the device name can be nostic plug. at runtime. Essentially, this used to identify the position Autosar and J1939 approach aims to utilize the of an exhaust gas tempera- come closer together SAE gets serious mechanism of dynamic ad- ture sensor – upstream or about dynamics dress allocation that has downstream of the catalytic The introduction of Auto- always existed in the com- converter, on the right or left sar in the passenger car in- Changes are also being mercial vehicle field, but side of a dual-flow exhaust dustry is ramping up quick- made in the area of Network has never really been im- system. Changes can be ly. Yet, there is also interest Management [5]. For a long plemented or used before. made to multiple ECUs in in exploiting the benefits of time now, the J1939-com- In conjunction with Net- sequence and activated at Autosar in commercial ve- mittee has been deliberat- work Management, the new- a specific point in time. This hicle and the agricultural ing over ways to handle the ly added Name Manage- could be helpful, for exam- machine markets. Howev- short supply of permanent- ment should be mentioned ple, in a case where multi- er, the special requirements ly assigned ECU address- for the sake of complete- ple ECUs of a network need of these markets have not es. This is especially prob- ness. This is a standard- to be assigned a new func- been a focus in the devel- lematic for manufacturers ized interface for changing tion simultaneously. opment of Autosar. There- fore, the Autosar versions released so far have very limited potential in these markets. In particular, the requirements of SAE J1939 cannot be mapped to the current Autosar concept, or only in a very limited way. The “static” approach of Autosar stands in con- trast to the “dynamic” be- havior of J1939. The Auto- sar architecture only allows fixed CAN-IDs (identifiers), i.e. there is a fixed alloca- tion between precisely one CAN-ID and one message layout. In contrast to this, a J1939-specific message Fig. 3: Autosar basic software from Vector contains the two J1939 transport protocols layout is only allocated to a BAM and CMDT specific part of the CAN-ID,

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INFO PEAK SYSTEMCOM known as the parameter the United Nations and doc- group (PG). Some of the umented in its Global Tech- other components of the nical Regulation 5 (GTR 5). 29-bit CAN-ID are dynamic ISO 27145 represents the and not defined at the time technical implementation of of configuration. Such a dy- GTR 5. It establishes tech- namic CAN-ID can be mod- nical constraints for WWH- eled in Autosar by creating OBD. WWH-OBD initially a separate static CAN-ID for targets the commercial ve- each combination of priori- hicle market, but eventual- ty, source address (SA) and ly it should be extended to Standardization destination address (DA) other vehicle industries as that can occur in a network. Fig. 4: The WWH-OBD is specified in ISO 27145 well. When all nodes of a ISO 27145 consists of J1939 network are known, More in-depth support OEMs Vector actively par- six parts. The current doc- and node addresses are al- of J1939 requirements is ticipates in efforts to spec- ument status is a Draft In- ready defined at the time of planned for the end of 2012 ify these J1939 extensions ternational Standard (DIS), configuration, it is relatively in Autosar release 4.1. The for Autosar. Today, Vector and a final version is antic- easy to map J1939 PGs to target group here includes already offers an Autosar ipated by the end of 2011. Autosar: In case of such a European and some North solution with a J1939 ex- The first step was to estab- static network, the ECU ad- American commercial ve- tension based on Autosar lish requirements for emis- dresses are fixed. There- hicle OEMs (original equip- release 4.0. It will soon be sions control and diagnos- fore source and destination ment manufacturer). used in production at one tic communications. This addresses are fixed, and so The primary extended large European commer- involved specifying the ve- it is possible to work with features being added to Au- cial vehicle OEM. The ex- hicle-side implementation, static CAN-IDs. To trans- tosar: tension for Autosar release data access and OBD data. mit data that is longer than X Support of multiple mes- 4.1 is currently in the devel- At this time, regional au- the 8 bytes available in a sages with the same lay- opment stage. thorities are still defining CAN frame, J1939-21 spec- out (the same parameter limit and threshold values; ifies two transport protocol group) Vehicle diagnostics harmonization will not occur (TP) variants. These are X Network M anagement using WWH-OBD until a later point in time. the broadcast announce per SAE J1939/81 with- For on-board diagnos- message (BAM) variant out dynamic NM, i.e. OBD is a diagnostic sys- tics in commercial vehicles, and connection mode data without AAC (arbitrary tem standardized by ISO; the two CAN-based proto- transfer (CMDT; also known address capable) one of its applications is to cols “Diagnostics on CAN” as RTS/CTS) variant. Both X Responses to a request monitor systems related to (ISO 15765-4) and J1939-73 of them are already defined message exhaust emissions control. are widely being used to- in Autosar release 4.0 and X Support for diagnostic Over the course of time, re- day. To enable a cost-ef- have been available since services gional standards were de- fective transition to WWH- December 2009. Therefore, X On-board diagnostics rived from this standard OBD, diagnostics over CAN Autosar release 4.0 already (WWH-OBD) via J1939 (e.g. ISO 15031), which will continue to be used at covers the requirements of have now been merged first. For the long term, di- many European commer- Together with large Euro- again into WWH-OBD. This agnostics over the Internet cial vehicle producers. pean commercial vehicle standard was initiated by Protocol (DoIP) should also be possible, which would enable access that is either wired over Ethernet or wire- less. Different than in the current OBD-II standard, WWH-OBD only utilizes services already defined as ISO 14229 Unified Diagnos- tic Services (UDS). No addi- tional OBD-specific servic- es are needed. Specifically, WWH-OBD requires sup- port of the UDS services. Effective at the begin- ning of 2014, all newly regis- tered heavy-duty commer- cial vehicles must conform to Euro VI standards, and so they must have WWH- OBD diagnostic capabili- Fig. 5: On-board diagnostics in commercial vehicles is implemented by CAN-based ty. Developments involving protocols new types of vehicles must

66 CAN Newsletter 1/2011      

      

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3523 Crosspoint, San Antonio, TX 78217 918.317.2615 www.cancapture.com/CA 1010545-CANCAPTURE-CIA in embedded software and development tools. References: [1] http://standards.sae.org [2] “CAN and open protocols in commercial vehicles”, CAN Newsletter 3/2005, pg. 60 Fig. 6: The WWH-OBD uses the diagnostic services from UDS [3] SAE, J1939-11, Physical layer, 250 kbits/s, Twisted Software/Tool fulfill standards one year solution has also become car technology aim to make shielded pair earlier by the beginning of available for implementing the development of J1939 [4] SAE, J1939-15, Reduced 2013. WWH-OBD diagnostics via ECUs more cost-effective. physical layer, 250 kbits/s, UDS services can be UDS. Vector, with its many years Unshielded twisted pair (UTP) implemented with CANbed- The described devel- of networking expertise, is [5] SAE, J1939-13, Off-board ded communication soft- opments in the J1939 field making a contribution by ac- diagnostic connector ware that also supports show how the standard tively participating in stan- [6] SAE, J1939-81, Network J1939, which is available continues to be adapted to dardization committees. In management from Vector and is practice- current requirements on a turn, developers of com- proven in many production regular basis. The transfer, mercial vehicle electronics implementations. Recently, extension and modification benefit from early imple- [email protected] a production-ready Autosar of concepts from passenger mentation of new standards [email protected]

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