WIG-09555

ELM327 OBD to RS232 Interpreter Description Features Almost all of the automobiles produced today Power Control with standby mode are required, by law, to provide an interface for the Universal serial (RS232) interface connection of diagnostic test equipment. The data transfer on these interfaces follow several standards, Automatically searches for protocols but none of them are directly usable by PCs or smart Fully configurable with AT commands devices. The ELM327 is designed to act as a bridge between these On-Board Diagnostics (OBD) ports Low power CMOS design and a standard RS232 serial interface. In addition to being able to automatically detect and interpret nine OBD protocols, the ELM327 also Connection Diagram provides support for high speed communications, a PDIP and SOIC low power sleep mode, and the J1939 truck and bus (top view) standard. It is also completely customizable, should you wish to alter it to more closely suit your needs. MCLR OBD Tx LED Vmeasure OBD Rx LED The following pages discuss all of the ELM327s features in detail, how to use it and configure it, as J1850 Volts RS232 Tx LED well as providing some background information on J1850 Bus+ RS232 Rx LED the protocols that are supported. There are also Memory CAN Rx schematic diagrams and tips to help you to interface Baud Rate CAN Tx to microprocessors, construct a basic scan tool, and LFmode ISO L to use the low power mode. VSS ISO K XT1 VDD Applications XT2 VSS VPW In RS232 Rx Diagnostic trouble code readers ISO In RS232 Tx Automotive scan tools PWM In PwrCtrl / Busy Teaching aids J1850 Bus- IgnMon / RTS Block Diagram 4.00 MHz Memory 6 MCLR Baud Rate 9 10 XT1 XT2 5 1 LFmode 7 Vmeasure 2 A/D 18 RS232Rx RS232 Converter Command Interface 17 RS232Tx and Protocol Interpreter ISO 15765-4 ISO 9141-2 SAE J1850 SAE J1939 ISO 14230-4 PWM & VPW PwrCtrl / Busy 16 Power Control IgnMon / RTS 15 23 24 21 22 12 3 4 14 13 11 25 26 27 28 OBD interfaces status LEDs ELM327DSI Elm Electronics Circuits for the Hobbyist 1 of 82 www.elmelectronics.comELM327 Contents Electrical Information Pin Descriptions........................................................................... 3 Unused Pins.................................................................................5 Ordering Information.................................................................... 5 Absolute Maximum Ratings......................................................... 5 Electrical Characteristics..............................................................6 Using the ELM327 Overview...................................................................................... 7 Communicating with the ELM327................................................ 7 AT Commands............................................................................. 9 AT Command Summary...............................................................9 AT Command Descriptions........................................................ 11 Reading the Battery Voltage...................................................... 28 OBD Commands........................................................................29 Talking to the Vehicle.................................................................30 Interpreting Trouble Codes........................................................ 32 Resetting Trouble Codes........................................................... 33 Quick Guide for Reading Trouble Codes................................... 33 Bus Initiation...............................................................................34 Wakeup Messages.....................................................................34 Selecting Protocols.................................................................... 35 OBD Message Formats..............................................................36 Setting the Headers................................................................... 38 Monitoring the Bus..................................................................... 41 CAN Receive Filtering - the CRA Command............................. 42 Using the CAN Mask and Filter..................................................43 Multiline Responses...................................................................44 CAN Message Formats..............................................................46 Restoring Order..........................................................................47 Advanced Features Altering Flow Control Messages................................................ 48 Using CAN Extended Addresses............................................... 49 SAE J1939 Messages................................................................50 Using J1939............................................................................... 52 The FMS Standard.....................................................................55 Programming Serial Numbers....................................................56 Saving a Data Byte.................................................................... 56 Programmable Parameters........................................................57 Programmable Parameter Summary......................................... 58 Using Higher RS232 Baud Rates...............................................63 Setting Timeouts - AT ST and AT AT Commands..................... 65 The Activity Monitor....................................................................66 Power Control............................................................................ 66 Design Examples Microprocessor Interfaces..........................................................70 Example Applications.................................................................71 Modifications for Low Power Standby Operation....................... 77 Misc. Error Messages and Alerts.........................................................78 Outline Diagrams....................................................................... 80 Copyright and Disclaimer...........................................................80 Index.......................................................................................... 81 2 of 82 ELM327DSI Elm Electronics Circuits for the Hobbyist www.elmelectronics.com