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1、SAE TECHNICAL PAPER SERIES J1939 Serial Vehicle Network Explanation and Tutorial Mark R. Stepper Cummins Engine Co., Inc. International Off-Highway however, the information was different from that on the main 1587 network. Author:Gilligan-SID:1178-GUID:12939514-141.211.175.139 The number of 31708 ne
2、tworks that can exist is unlimited; the same is true for 51939. That is, many networks can be created to handle specific tasks that are not of general interest to the primary 51939 network users and that require a significant percentage of the available bandwidth to perform one specific high speed c
3、ontrol task (FigureFollowing are two examples of specific high speed control tasks which would likely be performed on a separate network:(1)engine control performed by controllers which require individual cylinder event information to be commanded; and (2)electronic brake control performedbymultiple
4、 controllers which exchange high speed data specific to the braking task. As a general rule, significant bandwidth impact can be thought of as having a calculated percent utilization impact of 0.5 percent or more per second. The concept of bandwidth utilization is expanded later in this paper. Fuel
5、Variable Electronic Geometry PumpBrake Turbo I FIGUREExample of Network Configuration Network4 Controller Two EngineTractionBridge to Network2 ControllerControllerTrailer Network5 A 1.0ARCHITECTURAL OBSERVATIONS Controller Three Trailer Controller . Fare Box Two topics will be discussed with respect
6、 to the expected 31939 configuration. The first topic is that of network hier- archy and the planned level of interconnect between vehicle electronic subsystems. The second is network capacity; the various target percent utilizations will be discussed to gain further knowledge about the number of me
7、ssages available, assuming a given budget allocated for the defined update periods. PrimaryVehicleNetwork A Electronic Transmission Controller Onboard Bridge DashComputer MarqueeOperator ControllerDisplay 1.1NETWORK HIERARCHY -51939was developed to accommodate a Level Two network hierarchy connectio
8、n (Figure2).ALevel Two connection is one where major subsystems collect information necessary to perform their function and then provide the applicable information to the primary vehicle network. This level can be contrasted to a Level Three connection. In a Level Three connection the individual con
9、troller inputs (sensors, switches) and outputs (actuators, lamps, alarms) for all controllers are connected to a common vehicle network. In this case, the inputs and outputs associated with engine control would be connected on the same network as the inputs and outputs for the electronic brake signa
10、ls. As a result, the Level Three network would require more addresses to be available and the capability of more than 30 nodes per network. ALevel One network, on the other hand, would provide for connection of even fewer nodes than Level Two. For Level One, the different functions such as engine, t
11、ransmission and traction control are not connected to the network but instead one primary vehicle controller would be connectedto a two-or three-party network. In this case, the number of addresses and electrical nodes could be less than what is provided for in939. Author:Gilligan-SID:1178-GUID:1293
12、9514-141.211.175.139 Level One Two Engine Controller Computer Level Three I I. II TrailerIImplementIImplement Electronic Trailer BrakesI.D. Reefer Control I Electronic Trailer Brakes Reefer Control Throttle EngineSpeedsSpeeds BoostCoolant Position Activation Pressures Activation Pressures FIGURE2.Ex
13、ample of Network Hierarchy 1.2NETWORK CAPACITY-As a starting point forthe percent of network utilization that was targeted as an upper limit when incorporating all 51587, and newly defined parameters was 25 to 30 percent.However, because we are using the Controller Area Network (CAN) protocol, netwo
14、rk utilization could go up to 100 percent. It is known that once you reach 100 percent utilization the latency of messages does increase. That is why 51939 has defined one of the CAN identifier fields to be used for the priority of the messages. The following paragraphs explore target network transm
15、itted at the longest update period. Note that the term messagehas been used for two different purposes: when a specific CAN data frame identifier is assigned for a specific group of parameters to be sent at a given update period; and (2) when discussing the number of CAN data frames per second. 5193
16、9 defines that a group of parameters are labeled asparameter group numbers (PGN). Therefore, the phrase “the number of messages that can be transmitted in each update period range“really defines the number of individual that can be sent per the defined update period. utilization values and the corre
17、sponding number of available The last column,51939, presents an estimate messages in various update period ranges. The Budget made using the assumptions listed in the Notes section of cated Per Update Period column in Table 1 suggests there is a Table 1. The intent of including this column was to gi
18、ve some process to assure a portion of the available bandwidth is indication of how much of the network capacity is presently reserved for all update periods.The table is an example of consumed. just one possible budget allocation. One conclusion that can be drawn from Table1is that The table shows
19、the results of how many messages per there are a small number of messages to be defined in the the target network utilization percentage are able to be update period range of 10 to 20 millisecondsincomparison to mitted presuming the given budget. This budget was applied the number available from 0.1
20、0 to 1.00 second. Therefore, to target network utilizations of 40, 70 and 100 percent. The designers should strive to use larger update period messages Messages Available columns show the number of messages (greater than 200 ms update periods) whenever possible. that can be transmitted in each updat
21、e period range.The smaller number is if all messages are transmitted at the shortest update period; the larger number is if all messages are Author:Gilligan-SID:1178-GUID:12939514-141.211.175.139 Table1.Target Network Utilization 2.051939DOCUMENTS SUMMARY Table 2 details all of the documents that ha
22、ve been or are being defined under the title.Early on the subcom- mittee decided to use a labeling format where all documents would start withfollowed by a slash and then a digit number.The first of the two digits, in most cases, identifiestheapplicable International Organization of Systems Intercon
23、nection (ISOIOSI) layer The second of the two digits is used to identify additional capabilities J1939171, J1939173) or sometimes is used to indicate an alternate solutionversus 51939112 or 31939101 versus J 1939102). Table 2, column1is the document number and column 2 is the abbreviated docu- ment
24、title. See the reference list at the end of this paper for the complete titles and the most current documents available. Update Period (Seconds) .OO Total Current 51939 Notes Budget Allocated Per Update Period 50% 30% 20% 100% Mes- sages Used 10 20 5 5 85 IMessages per time or percent allocated were
25、 truncated. Therefore, the numbers in the table present numbers and thus result in target network utilizations less than 40, 70 and 100 percent,736 instead of 781 messages per second. A.7810.5=390 messages per second budgeted 390 messages per second100 updates per second for msec period messages=3 m
26、essages available 390 messages per second50 updates per second for 20 msec period messages =7 messages available 750=350 messages per second when truncated B.7810.3=234 234 messages per second50 updates per second for 20 msec period messages=4messages available 234 messages per secondupdates per sec
27、ond formsec period messages =23 messages available 23 C.781*0.2=156 156 messages per secondupdates per second for msec period messages=messages available 156 messages per second1update per second forperiod messages=156 messages available 156*=156 2. Eight-byte messages were assumed. Message time use
28、d=(128 bits per message)*(4per bit)=512 psec per message For example: one second divided by 512 psec results in 1,953 messages per second 40% of 1,953=781 70% of 1,953=1367 3. The messages defined inwere inclusive through the April 1997 addendum. The messages per update period range were countedas20
29、 ms. 100 ms and second messages. For instance, the TC1message is defined to be sent every 50 ms so it was counted as two 100 ms messages. This technique was used on messagesinall three update period ranges. Note: as-needed or on-request messages were not included. 4. Assumed EECI was sent at 5 ms, T
30、SCI sent from transmission and traction control to engine.sent from the transmission to retarder, TCI sent from traction control to transmission. Result- ing 500 200 5 5 755 Target Network Utilization 100 Percent40 Percent Messages Available 9-19 11-58 39-391 59468 70 Percent Messages Available 3-7
31、4-23 15-156 22-186 ing (Max= 1953) 950 580 391 1921 Messages Available 6-13 1 27-273 41-327 ing (Max= 781) 350 230 156 736 Result- ing (Max= 1367) 650 410 273 1333 Author:Gilligan-SID:1178-GUID:12939514-141.211.175.139 Table2.51939Documents3.0SYNOPSIS O F THE STANDARDS Figure3uses theseven layer mod
32、el to identify the association of the SAE Truck and Bus Recommended Practices to this model It also shows what parts of the model the CAN protocol satisfies. Some of the questions this figure attempts to resolve are:(1)If you define that you are using CAN, what else do you need?; (2)What section of
33、covers a specific portion of the ISOIOSI model?;(3) What kind of applications will the51939primary vehicle network support?; and (4)How does51939compare to the 1587, 1708and922capabilities? Document Number 31939101 51939112 193912 193913 193917 939172 1939173 51939181 52214 Table3summarizes the defi
34、nition of 51939as of mid- 1997.This definition is discussed with references to the ISOIOSI model in an effort to use well-defined, industry agreed-upon terms to achieve a more common understanding. The ISOIOSI model identifies the communications task to be covered by seven defined layers: physical,
35、data link, network, transport, session, presentation and application layers.This paper presents the layers applicable to51939:physical, data link, network and application. Abbreviated Document Title RP for Serial Control and Communications Vehicle Network Truck and Bus Specific Physical Layer-Twiste
36、d Shielded Pair Physical Layer-Twisted Quad Data Link Layer Network Layer Applications Layer Virtual Terminal Application Layer, Diagnostics Network Management VEPS,J1939Specific Version Needed Table3presents a synopsis which compares the Recommended Practices with SAE Recommended Practices 51922and
37、587.It is organized in four major groupings to show the physical, data link, network and application layers. Controls Proprietary Includes all sharing andcommunications functions of diagnostics5 Proprietary Proprietary t SAE I SAE Figure3.SAE Documents Mapped toModel 5 CAN 898 (CAN) Author:Gilligan-
38、SID:1178-GUID:12939514-141.211.175.139 Table3.Synopsisof 51939,51922and Subject Area Networks Physical Layer 51587 andand 51939112 Character wide bits). random, destructive 9.600 20120 Bus 40 meters 40 meters None None Twisted pair 6 or 8 pins Network arbitration access Bitssecond Maximum nodes Topo
39、logy Bus length Stub length Stub connector Termination resistor Cabling Diagnostic connector Bit wide, random, nondestructive 250,000 3 0 Linear bus 40 meters3feet) meter (3.3 feet) 3-pin 2 required: passiveactive twisted shielded pair with drain 2 twisted quad 9 pins Data Link Layer Character wideb
40、its), random, destructive 9,600 4 1 20 Bus 40 meters 40 meters None None Twisted pair NIA MID8 bits 8 bits Data8-144 bits Data Checksum8 bits 1-9 512 4 to 21characters (4 to 210 bits) format Labels per message Labels available Parameters per label (min to max) Message length Priority3bits Resewedbit
41、 Data page1bit PDU format8 bits PDU specific8 bits Source address8 bits Databits CRCbits 8672 6 (1-32) 8 to bytes (-64 to 150 bits) Network Layer MID8bits Data8-160 bits Checksum8 bits 18 8 (1-14) 3 to 22 characters (30 to 220 bits) Message Number of database management functions Number of database
42、statistics NIA NIA NIA PGNpass or block 6 Application Layer NIA NIA NIA Application categories Update period of engines main control message Labels assigned Addresses assigned available Network utilization Control, information sharing, diagnos- tics, multiplexing and proprietary 5-35 ms Reserved for
43、 Dynamic 39:1025 100%-40% Limited controls for four subsystems 50 ms 181 67%67% sharing, diagnos- tics and proprietary Fast update period isms 249 109 67% Author:Gilligan-SID:1178-GUID:12939514-141.211.175.139 4.0 51939DOCUMENTS The following paragraphs discuss the documents. A brief description is
44、provided for what is contained in or planned for each of the documents. For each of the docu- ments, the documentation status is given. 4.151939RECOMMENDED PRACTICE FOR A CONTROLANDCOMMUNICATIONS VEHICLE NETWORK-This SAE document is com- pleting the balloting process and should be published for the
45、first time by the end of 1997. The J 1939 document provides a list of all of thedocuments that are planned.It provides a brief tutorial about the overall set of documents and the basic operation of the network. It contains: Glossary of terms used in the J 1939 documents Name definitions and assignme
46、nts for associating addresses to vehicle subsystem functions,engine, transmission Address assignments for identifying the source! destination of a message aParameter group number assignments for identifying parameters and commands aSuspect parameter number (SPN) assignments for use during system dia
47、gnosis and maintenance Request forms for users to request addresses, names,and aExample of vehicle powertrain control sequences for transmission shift, traction control and brake events There are two primary ways to procure addresses for network operation:using the preferred address that has been as
48、signed in SAE 51939 tables B2 through B9, or (2) using a dynamically acquired address.When using the dy- namically acquired address approach, all electronic control units (ECU) that want to communicate with a specific ECU are required to keep an address-to-name association table. Note that one purpo
49、se of the name is to identify the primary function an ECU performs. Preferred address assignments are made according to the following allocation: to 127Assigned to devices that are most commonly used on all vehicles or offboard) 128 to 247 Reserved for industry-specific assignment and dynamically acquired addresses 248 to 253Assigned to devices that are most commonly used on all vehicles or offboard) 254Null address 255Global address Preferred addresses to 127 and 248 to 253 use one address per device. They are assigned to devices that are on the main vehicle and perform a subsystem function
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