SAE J 2740-2005 General Motors UART Serial Data Communications《一般发动机UART连续数据通信》.pdf

1、 SURFACE VEHICLE INFORMATION REPORT General Motors UART Serial Data Communications 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 su

2、itability 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. Co

3、pyright 2005 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

4、 ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA) Fax: 724-776-0790 Email: custsvcsae.org SAE WEB ADDRESS: http:/www.sae.org Issued 2005-12 J2740 ISSUED DEC2005 TABLE OF CONTENTS 1. Scope . 3 1.1 Rationale 3 2. References. 3 2.1 Applicable Publications 3 2.1.1 SAE Pub

5、lications 3 3. Definitions. 3 3.1 Master ECU 3 3.2 Serial Data Bus 3 3.3 Slave ECU 3 3.4 Tester . 4 4. Acronyms . 4 5. System Elements . 4 5.1 Master ECU 5 5.2 Slave ECU 5 5.3 Tester . 6 5.4 Data Link Connector 6 6. System Element Moding 6 7. Communication Protocol and Timing. 6 7.1 Bus Moding 7 7.2

6、 Message Structure. 7 7.2.1 Data Bit. 7 7.2.2 Data Byte 7 7.2.3 Idle Byte . 7 7.2.4 Message Format 7 7.2.4.1 Message Identification Byte . 8 SAE J2740 Revised DEC2005 - 2 - 7.2.4.2 Message Length Byte 8 7.2.4.3 Data Bytes. 8 7.2.4.4 Checksum Byte 8 7.2.5 Message Diagram 9 7.3 Timing. 9 7.3.1 Bit Tim

7、ing . 9 7.3.2 Byte Timing 9 7.3.3 Message Timing. 10 7.3.3.1 Master ECU Polling10 7.3.3.2 Nonpolling Master ECU 12 7.3.3.3 Master ECU Response 12 7.3.3.4 Slave ECU Response 12 7.3.3.5 Tester Response 13 7.4 Serial Bus Errors 13 7.4.1 General. 13 7.4.2 Erroneous Messages . 13 7.4.2.1 Wrong MIB Code13

8、 7.4.2.2 Invalid Message Length Byte. 13 7.4.2.3 Framing Error . 13 7.4.2.4 Overrun Error . 14 7.4.2.5 Noise Flag 14 7.4.2.6 Sum Check. 14 7.4.2.7 No Polling Response 14 8. System Messages 14 8.1 Normal Mode 14 8.2 ALDL (Assembly Line Diagnostic Link) Mode 15 8.2.1 Message Identification Byte . 15 8

9、.2.2 ALDL Function Modes 15 8.2.3 ALDL Mode Message Structure. 15 8.2.4 ALDL Mode Messages. 16 8.2.4.1 Tester Polling Message 16 8.2.4.2 Tester Polling Response Message 16 9. Electrical Parameters.17 9.1 Design Objectives 17 9.1.1 Line Noise Rejection 17 9.1.2 Short Circuit Protection 17 9.1.3 Power

10、 or Ground Failures 17 9.1.4 Disruptive Transients .18 9.1.5 Data Output 18 9.1.6 Bus Pull-Up Resistor18 9.2 General Requirements. 18 9.2.1 Single Wire Data Bus. 18 9.2.2 Discrete Circuit. 19 9.2.2.1 Transmit - Receive Circuit Diagram. 20 9.2.2.2 Layout Considerations . 20 9.2.2.3 Test Specification

11、s. 21 SAE J2740 Revised DEC2005 - 3 - 1. Scope This Technical Information Report defines the General Motors UART Serial Data Communications Bus, commonly referred to as GM UART. This document should be used in conjunction with SAE J2534-2 in order to enhance an SAE J2534 interface to also provide th

12、e capability to program ECUs with GM UART. SAE J2534-1 includes requirements for an interface that can be used to program certain emission-related Electronic Control Units (ECUs) as required by U.S. regulations, and SAE J2534-2 defines enhanced functionality required to program additional ECUs not m

13、andated by current U.S. regulations. The purpose of this document is to specify the requirements necessary to implement GM UART in an enhanced SAE J2534 interface intended for use by independent automotive service facilities to program GM UART ECUs in General Motors vehicles. 1.1 Rationale Not appli

14、cable. 2. References 2.1 Applicable Publications The following publications form a part of this specification to the extent specified herein. Unless otherwise indicated, the latest version of SAE publications shall apply. 2.1.1 SAE PUBLICATIONS Available from SAE, 400 Commonwealth Drive, Warrendale,

15、 PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. SAE J2534-1Recommended Practice for Pass-Thru Vehicle Programming SAE J2534-2Recommended Practice for Optional Pass-Thru Features 3. Definitions 3.1 Master ECU An ECU that can send and receive messa

16、ges on the serial data bus, and that controls the flow of messages on the data bus 3.2 Serial Data Bus A physical connection between devices that comprise a vehicle system used to send and receive message bytes sequentially 3.3 Slave ECU An ECU on the serial data bus that receives requests from the

17、Master ECU and performs the requested functions, and sends messages only when requested by a Master ECU or Tester SAE J2740 Revised DEC2005 - 4 - 3.4 Tester A device, external to the vehicle, that has the capability to connect to the serial data bus through a data link connector (DLC) and assume the

18、 role of a Master ECU, primarily for the purpose of diagnostices or reprogramming 4. Acronyms ALDL Assembly Line Diagnostic Link DLC Data Link Connector ECU Electronic Control Unit LSB Least Significant Bit MIB Message Identification Byte MSB Most Significant Bit NRZ Non-Return to Zero UART Universa

19、l Asynchronous Receiver/Transmitter 5. System Elements The elements of a GM UART serial data bus system are shown in Figure 1. A vehicle system is composed of a Master ECU, the Serial Data Bus, a group of optional Slave ECUs, and a Data Link Connector which permits access to the Serial Data Bus by e

20、xternal test devices. External test devices, called Testers, can be a Service Tester (often called a Scan Tool), an Assembly Line Tester, or an SAE J2534 pass-thru programming interface. FIGURE 1SYSTEM ELEMENTS Tester Data Link ConnectorVehicle SystemMasterECUSlave ECU #1Slave ECU #2Slave ECU #nSeri

21、al Data Bus SAE J2740 Revised DEC2005 - 5 - The functionality of these elements are contained in the following paragraphs. 5.1 Master ECU A Master ECU is an ECU or Tester that is in control of the bus. The Master ECU shall perform transmit and receive functions. The major characteristic which distin

22、guishes the Master ECU from a Slave ECU is that it controls the traffic on the serial bus. The Master ECU shall control which device has control of the bus via a cyclic transmission of polling messages. Normal operation is for the Master ECU to transmit a message and then receive a valid response me

23、ssage transmitted by the proper Slave ECU. The Master ECU will transmit the next message at the scheduled time. The sequence of messages may vary from application to application and from model year to model year. The Master ECU may also periodically transmit an ALDL polling message to determine if t

24、here is a Tester connected to the serial data bus that needs to take control of the serial data bus. If a Tester responds to this ALDL polling message, the Master ECU relinquishes control of the serial data bus to the Tester and becomes a Slave ECU. When the system does not contain any Slave ECUs, t

25、he Master ECU may not execute a scheduled polling sequence. In this case, the only possible communications would be between the Master ECU and a Tester. The Master ECU would then be in a listening mode and respond only when interrogated by the Tester. Its function is then equivalent to a Slave ECU.

26、The Master ECU may “Broadcast” information per a schedule, with no response from any other device (except an ALDL Tester) on the link. A Master ECU in control of the bus can be moded into an ALDL Mode by a Tester when it responds to the appropriate polling message issued by the Master ECU. That resp

27、onse shall typically be a command to disable normal communications via a “Mode 8” function mode number in the response message. The actual response message required by an interface to become Master ECU is defined by the programming application using the PassThruIoctl function specified in SAE J2534-

28、2. The Master ECU will then discontinue executing its normal polling sequence, relinquish control to the Tester, and the Tester then becomes the Master ECU. 5.2 Slave ECU A Slave ECU is an ECU on the serial bus that performs the receiver functions. If a Slave ECU is also designed to transmit on the

29、serial bus, it shall only perform the transmit functions when requested by the Master ECU. The major feature which distinguishes a Slave ECU from the Master ECU is that it does not perform the bus traffic control function. A Slave ECU shall only transmit its preassigned message(s) after the receipt

30、of a valid request message. A given Slave ECU can be programmed to respond to more than one request. Once a Slave ECU has received the end of a valid message instructing it to transmit, it must respond within the timing defined in the Communication Protocol and Timing section. A Slave ECU which perf

31、orms the transmit function can be moded into the ALDL Mode, similar to the Master ECU. This requires that if a Master ECU is present in the system, it must be idled and the Tester assumes the role of the Master ECU. SAE J2740 Revised DEC2005 - 6 - 5.3 Tester A Tester is external to the vehicle and i

32、s not part of the normal vehicle operating configuration. A Tester is defined to have the capability to connect to the serial data bus through a data link connector (DLC), receive and transmit information on the serial data bus, and to assume the role of the Master ECU. The Tester is normally used t

33、o request data from the system devices on the vehicle and control these devices for the purpose of verifying system operation and diagnosing malfunction conditions, or for purposes of reprogramming the ECU. 5.4 Data Link Connector All GM vehicles built since the 1996 model year, and a few built duri

34、ng the 1995 model year, have been equipped with an SAE J1962 connector. GM UART uses either Pin 9 or Pin 1 of this connector. Most GM vehicles with serial data links built prior to the 1996 model year are equipped with a GM specific 12 pin connector. SAE J2534-2 includes GM UART pin usage for both o

35、f these connectors. 6. System Element Moding Each device of the system shall contain all, or some subset of, the following operating modes: Normal All normal control or display functions are being performed. If a scheduled polling sequence is a part of the system design, it is being executed in the

36、Normal Mode. It is entered upon power-up or from exiting the ALDL Mode. ALDL This mode is entered from the Normal Mode. It is entered upon receipt of a Tester command message requesting that the device enter an ALDL Mode. Transmit This mode is entered when a message is to be sent from either the Nor

37、mal Mode or the ALDL Mode. Receive This mode is entered when a message is being received for either the Normal Mode or the ALDL Mode. 7. Communication Protocol and Timing The serial data bus is normally implemented as an 8192 baud (bit per second), half duplex, Non-Return to Zero (NRZ), Universal As

38、ynchronous Receiver/Transmitter (UART) type. Different baud rates are used for some vehicles, but that will be controlled and set in the interface by the programming application using SAE J2534-2 functions. The following paragraphs specify the protocol and timing details. SAE J2740 Revised DEC2005 -

39、 7 - 7.1 Bus Moding There are three states that the serial data bus may occupy: Active A transmitter of one of the system devices is active and transmitting information. The bus may either be in a logic “1” or logic “0” state. Inactive There is no active transmitter connected to the bus. The bus is

40、in a logic “1” state as a result of the electrical configuration. Idle A transmitter of one of the system devices is active and transmitting a 10-bit byte, consisting of all logic “1”s. 7.2 Message Structure 7.2.1 DATA BIT A high voltage state shall indicate a logic “1” condition and a low voltage s

41、tate shall indicate a logic “0” condition. High and low voltage states are based on 5-volt logic elements and are specified in detail in the Electrical Parameters section. Voltage states that define logic level are those at the center of the bit interval. 7.2.2 DATA BYTE A Data Byte shall consist of

42、 ten bit times. The first bit shall always be a logic zero and is called the Start Bit. The last (tenth) bit in the byte shall always be a logic one and is called the Stop Bit. The eight center bits are data bits and are transmitted Least Significant Bit (LSB) first. A Start Bit must always be prece

43、ded by at least one logic one bit time (either the Stop Bit of the preceding byte or an idle bus state). The eight data bits represent the data value in binary form. 7.2.3 IDLE BYTE A byte consisting of ten bits, all of which are a logic “1”, shall precede any message string of data bytes. This shal

44、l be initiated within the transmitting device as a preamble to the message. 7.2.4 MESSAGE FORMAT All communications on the serial data bus are performed using the following message format in Figure 2: SAE J2740 Revised DEC2005 - 8 - Byte Description 1 Message Identification Byte 2 Message Length (N

45、+ 85) 3 to N + 2 N Data Bytes (N may be Zero) N + 3 Checksum Where N is the number of data bytes. FIGURE 2MESSAGE FORMAT The following sections define the message bytes. 7.2.4.1 Message Identification Byte Each message contains a Message Identification Byte (MIB) which identifies the message. A sing

46、le communications device may be able to transmit and receive several different messages, each with a unique MIB. The MIB codes shall be assigned by the vehicle manufacturer in the appropriate vehicle system specificiation. Any receiver can listen and extract data from any message. Each Slave ECU uni

47、t which is designed to transmit on the bus may only do so after it has received a complete valid message which begins with its preassigned MIB. The total number of unique MIB codes is limited to 254. MIB codes of $00 (hexadecimal notation) and $FF shall not be used. 7.2.4.2 Message Length Byte The M

48、essage Length Byte indicates the total number of data bytes in the remainder of the message, plus 85. The number of data bytes in one message shall be in the range of 0 to 170. Thus a valid message length byte must lie in the range of 85 to 255. Many messages with no data bytes are possible; for suc

49、h messages, the Message Length byte would contain 0101 0101 ($55). This pattern has been selected because, under an abnormally severe noise environment, there is a higher probability that a noise contaminated message will be detected as such. 7.2.4.3 Data Bytes The data bytes contain the application specific data. The meaning or interpretation of the data is a function of the predetermined message, with predetermined order and predetermined scaling. Detailed requirements vary from application to application and model year to model year. 7.2.4.4 Checksum Byte T