ELM327 OBD to RS232 Interpreter - Elm Electronics

1 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.

2 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. The following pages discuss all of the ELM327 's Vmeasure OBD Rx LED. 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.

3 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 MHz Baud Rate 6 Memory MCLR. XT1 9 10 XT2. 5 1. LFmode 7 Vmeasure 2. A/D. RS232Rx 18. RS232 . command Converter RS232Tx Interface 17 and Protocol Interpreter ISO 15765-4 ISO 9141-2 SAE J1850.

4 PwrCtrl / Busy 16 SAE J1939 ISO 14230-4 PWM & VPW. Power IgnMon / RTS 15 Control 23 24 21 22 12 3 4 14 13 11. 25 26 27 28. OBD interfaces status LEDs ELM327 DSJ Elm Electronics Circuits for the Hobbyist 1 of 94. ELM327 . Contents The Basics 1. 1. Block Connection 1. Pin 4. Unused Absolute Maximum 6. Electrical Using the ELM327 8. Communicating with the 8. AT 10. AT command AT command 12. Reading the Battery 29. OBD 30. Talking to the Bus Interpreting Trouble 34. Resetting Trouble 35. Quick Guide for Reading Trouble 35. Selecting 36. OBD Message Setting the 39. Multiline 42.

5 CAN Message 44. Multiple PID Response Pending 45. CAN Receive Filtering - the CRA 46. Using the CAN Mask and Monitoring the 48. Restoring Advanced Features Using Higher RS232 Baud Setting Timeouts - the AT ST and AT AT 52. SAE J1939 Using 55. The FMS The NMEA 2000 59. Periodic (Wakeup) 59. Altering Flow Control 60. Using CAN Extended 61. CAN Input Frequency 62. ELM327 DSJ Elm Electronics Circuits for the Hobbyist 2 of 94. ELM327 . Contents Advanced Features Programming Serial (continued) Saving a Data 63. The Activity Power 64. Programmable 68. Programmable Parameter 69.

6 Design Discussions Maximum CAN Data 74. Microprocessor Upgrading Example Figure 9 - An OBD to USB 80. Figure 10 - Parts List for Figure 81. Figure 11 - A Low Speed RS232 81. Figure 12 - A High Speed RS232 82. Figure 13 - An Alternative USB 82. Figure 14 - Connecting to a Modifications for Low Power Standby 84. Misc. Information Error Messages and Version Outline 92. Ordering 92. Copyright and 92. 93. ELM327 DSJ Elm Electronics Circuits for the Hobbyist 3 of 94. ELM327 . Pin Descriptions MCLR (pin 1). A momentary (>2 sec) logic low applied to this input return and a linefeed character.

7 If it is at a low level, will reset the ELM327 . If unused, this pin should be lines will be terminated by a carriage return only. connected to a logic high (VDD) level. This behaviour can always be modified by issuing an AT L1 or AT L0 command . Vmeasure (pin 2). This analog input is used to measure a 0 to 5V VSS (pin 8). signal that is applied to it. Care must be taken to Circuit common must be connected to this pin. prevent the voltage from going outside of the supply levels of the ELM327 , or damage may occur. If it is XT1 (pin 9) and XT2 (pin 10). not used, this pin should be tied to either VDD or VSS.

8 A MHz oscillator crystal is connected between these two pins. Loading capacitors as required by J1850 Volts (pin 3) the crystal (typically 27pF each) will also need to be This output can be used to control a voltage supply connected between each of these pins and circuit for the J1850 Bus+ output. The pin normally outputs common (Vss). a logic high level when a nominal 8V is required (for Note that this device has not been configured for J1850 VPW), and a low level for 5V (for J1850 operation with an external oscillator it expects a PWM), but this can be changed with PP 12.

9 If this crystal to be connected to these pins. Use of an switching capability is not required for your external clock source is not recommended. Also, application, this output can be left open-circuited. note that this oscillator is turned off when in the Low Power or standby' mode of operation. J1850 Bus+ (pin 4). This active high output is used to drive the VPW In (pin 11). J1850 Bus+ Line to an active level. Note that this This is the active high input for the J1850 VPW data signal does not have to be used for the Bus- Line (as signal. When at rest (bus recessive) this pin should was the case for the ELM320), since a separate be at a low logic level.

10 This input has Schmitt trigger J1850 Bus- drive output is provided on pin 14. wave shaping, so no special amplification is required. Memory (pin 5). This input controls the default state of the memory ISO In (pin 12). option. If this pin is at a high level during power-up or This is the active low input for the ISO 9141 and reset, the memory function will be enabled by ISO 14230 data signal. It is derived from the K Line, default. If it is at a low level, then the default will be and should be at a high logic level when at rest (bus to have it disabled. Memory can always be enabled recessive).