ELM327 OBD to RS232 Interpreter Description Features Almost all of the automobiles produced today are required, by law, to provide an interface for the connection of diagnostic test equipment. The data transfer on these interfaces follow several standards, but none of them are directly usable by PCs or smart devices. The ELM327 is designed to act as a bridge between these On-Board Diagnostics (OBD) ports and a standard RS232 serial interface. In addition to being able to automatically detect and interpret nine OBD protocols, the ELM327 also provides support for high speed communications, a low power sleep mode, and the J1939 truck and bus standard. It is also completely customizable, should you wish to alter it to more closely suit your needs. The following pages discuss all of the ELM327’s features in detail, how to use it and configure it, as well as providing some background information on the protocols that are supported. There are also schematic diagrams and tips to help you to interface to microprocessors, construct a basic scan tool, and to use the low power mode. • Power Control with standby mode • Universal serial (RS232) interface • Automatically searches for protocols • Fully configurable with AT commands • Low power CMOS design Connection Diagram PDIP and SOIC (top view) MCLR OBD Tx LED Vmeasure OBD Rx LED J1850 Volts RS232 Tx LED J1850 Bus+ RS232 Rx LED Memory CAN Rx Baud Rate CAN Tx LFmode ISO L Applications • Diagnostic trouble code readers • Automotive scan tools • Teaching aids Block Diagram VSS ISO K XT1 VDD XT2 VSS VPW In RS232 Rx ISO In RS232 Tx PWM In PwrCtrl / Busy J1850 Bus- IgnMon / RTS 4.00 MHz Baud Rate LFmode 6 Memory 5 7 XT1 9 XT2 10 MCLR 1 Vmeasure 2 RS232Rx 18 RS232Tx 17 PwrCtrl / Busy 16 IgnMon / RTS 15 RS232 Interface Command and Protocol Interpreter Power Control A/D Converter ISO 15765-4 SAE J1939 23 25 26 27 24 28 ISO 9141-2 ISO 14230-4 21 22 12 SAE J1850 PWM & VPW 3 4 14 13 11 OBD interfaces status LEDs ELM327QSJ Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com 1 of 8 ELM327 Pin Descriptions MCLR (pin 1) A momentary (>2µsec) logic low applied to this input will reset the ELM327. If unused, this pin should be connected to a logic high (VDD) level. Vmeasure (pin 2) This analog input is used to measure a 0 to 5V signal that is applied to it. Care must be taken to prevent the voltage from going outside of the supply levels of the ELM327, or damage may occur. If it is not used, this pin should be tied to either VDD or VSS. J1850 Volts (pin 3) This output can be used to control a voltage supply for the J1850 Bus+ output. The pin normally outputs a logic high level when a nominal 8V is required (for J1850 VPW), and a low level for 5V (for J1850 PWM), but this can be changed with PP 12. If this switching capability is not required for your application, this output can be left open-circuited. J1850 Bus+ (pin 4) This active high output is used to drive the J1850 Bus+ Line to an active level. Note that this signal does not have to be used for the Bus- Line (as was the case for the ELM320), since a separate J1850 Bus- drive output is provided on pin 14. return and a linefeed character. If it is at a low level, lines will be terminated by a carriage return only. This behaviour can always be modified by issuing an AT L1 or AT L0 command. VSS (pin 8) Circuit common must be connected to this pin. XT1 (pin 9) and XT2 (pin 10) A 4.000 MHz oscillator crystal is connected between these two pins. Loading capacitors as required by the crystal (typically 27pF each) will also need to be connected between each of these pins and circuit common (Vss). Note that this device has not been configured for operation with an external oscillator – it expects a crystal to be connected to these pins. Use of an external clock source is not recommended. Also, note that this oscillator is turned off when in the Low Power or ‘standby’ mode of operation. VPW In (pin 11) This is the active high input for the J1850 VPW data signal. When at rest (bus recessive) this pin should be at a low logic level. This input has Schmitt trigger wave shaping, so no special amplification is required. Memory (pin 5) This input controls the default state of the memory option. If this pin is at a high level during power-up or reset, the memory function will be enabled by default. If it is at a low level, then the default will be to have it disabled. Memory can always be enabled or disabled with the AT M1 and AT M0 commands. ISO In (pin 12) This is the active low input for the ISO 9141 and ISO 14230 data signal. It is derived from the K Line, and should be at a high logic level when at rest (bus recessive). No special amplification is required, as this input has Schmitt trigger wave shaping. Baud Rate (pin 6) This input controls the baud rate of the RS232 interface. If it is at a high level during power-up or reset, the baud rate will be set to 38400 (or the rate that has been set by PP 0C). If at a low level, the baud rate will be initialized to 9600 bps. PWM In (pin 13) This is the active low input for the J1850 PWM data signal. It should normally be at a high level when at rest (ie. bus recessive). This input has Schmitt trigger wave shaping, so no special amplification is required. LFmode (pin 7) This input is used to select the default linefeed mode to be used after a power-up or system reset. If it is at a high level, then by default messages sent by the ELM327 will be terminated with both a carriage J1850 Bus- (pin 14) This active high output is used to drive the J1850 Bus- Line to an active (dominant) level for J1850 PWM applications. If unused, this output can be left open-circuited. ELM327QSJ Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com 2 of 8 ELM327 Pin Descriptions (continued) IgnMon / RTS (pin 15) This input pin can serve one of two functions, depending on how the Power Control options (PP 0E) are set. If both bit 7 and bit 2 of PP 0E are ‘1’s, this pin will act as an Ignition Monitor. This will result in a switch to the Low Power mode of operation, should the IgnMon signal go to a low level, as would happen if the vehicle’s ignition were turned off. An internal ‘debounce’ timer is used to ensure that the ELM327 does not shut down for noise at the input. When the voltage at pin 15 is again restored to a high level, and a time of 1 or 5 seconds (as set by PP 0E bit 1) passes, the ELM327 will perform a ‘Warm Start’ and return to normal operation. A low to high transition at pin 15 will in fact restore normal operation, regardless of the setting of PP 0E bit 2, or whether pin 15 was the initial cause for the low power mode. This feature allows a system to control how and when it switches to low power standby operation, but still have automatic wakeup by the ignition voltage, or even by a pushbutton. If either bit 7 or bit 2 of PP 0E are ‘0’, this pin will function as an active low ‘Request To Send’ input. This can be used to interrupt the OBD processing in order to send a new command, or as previously mentioned, to highlight the fact that the ignition has been turned off. Normally kept at a high level, this input is brought low for attention, and should remain so until the Busy line (pin 16) indicates that the ELM327 is no longer busy, or until a prompt character is received (if pin 16 is being used for power control). This input has Schmitt trigger wave shaping. By default, pin 15 acts as the RTS interrupt input. PwrCtrl / Busy (pin 16) This output pin can serve one of two functions, depending on how the Power Control options (PP 0E) are set. If bit 7 of PP 0E is a ‘1’ (the default), this pin will function as a Power Control output. The normal state of the pin will be as set by PP 0E bit 6, and the pin will remain in that state until the ELM327 switches to the Low Power mode of operation, when the output changes to the opposite level. This output is typically used to control enable inputs, but may also be used for relay circuits, etc. with suitable buffering. The ELM327QSJ discussion on page 84 (‘Modifications for Low Power Standby Operation’) provides more detail on how to use this output. If bit 7 of PP 0E is a ‘0’, pin 16 will function as a ‘Busy’ output, showing when the ELM327 is actively processing a command (the output will be at a high level), or when it is idle, ready to receive commands (the output will be low). By default, bit 7 of PP 0E is ‘1’, so pin 16 provides the Power Control function. RS232Tx (pin 17) This is the RS232 data transmit output. The signal level is compatible with most interface ICs (the output is high when idle), and there is sufficient current drive to allow interfacing using only a PNP transistor, if desired. RS232Rx (pin 18) This is the RS232 receive data input. The signal level is compatible with most interface ICs (when at idle, the level should be high), but can be used with other interfaces as well, since the input has Schmitt trigger wave shaping. VSS (pin 19) Circuit common must be connected to this pin. VDD (pin 20) This pin is the positive supply pin, and should always be the most positive point in the circuit. Internal circuitry connected to this pin is used to provide power on reset of the ELM327 processor, so an external reset signal is not required. Refer to the Electrical Characteristics section for further information. ISO K (pin 21) and ISO L (pin 22) These are the active high output signals which are used to drive the ISO 9141 and ISO 14230 buses to an active (dominant) level. Many new vehicles do not require the L Line – if yours does not, you can simply leave pin 22 open-circuited. CAN Tx (pin 23) and CAN Rx (pin 24) These are the two CAN interface signals that must be connected to a CAN transceiver IC (see the Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com 3 of 8 ELM327 Pin Descriptions (continued) Example Applications section for more information). If unused, pin 24 must be connected to a logic high (VDD) level. RS232 Rx LED (pin 25), RS232 Tx LED (pin 26), OBD Rx LED (pin 27) and OBD Tx LED (pin 28) These four output pins are normally high, and are driven to low levels when the ELM327 is transmitting or receiving data. These outputs are suitable for directly driving most LEDs through current limiting resistors, or interfacing to other logic circuits. If unused, these pins may be left open-circuited. Note that pin 28 can also be used to turn off all of the Programmable Parameters, if you can not do so by using the normal interface - see page 69 for details. Unused Pins When people only want to implement a portion of what the ELM327 is capable of, they often ask what to do with the unused pins. The rule is that unused outputs may be left open-circuited with nothing connected to them, but unused inputs must be terminated. The ELM327 is a CMOS integrated circuit that can not have any inputs left floating (or you might damage the IC). Connect unused inputs as follows: Pin 1 2 5 6 7 11 12 13 15 18 24 Level H H* H* H* H* H* L* L* H H H Note that the inputs that are shown with an asterisk (*) may be connected to either a High (VDD) or a Low (VSS) level, but the level shown is preferred. Absolute Maximum Ratings Storage Temperature....................... -65°C to +150°C Ambient Temperature with Power Applied....................................-40°C to +85°C Voltage on VDD with respect to VSS..... -0.3V to +7.5V Note: These values are given as a design guideline only. The ability to operate to these levels is neither inferred nor recommended, and stresses beyond those listed here will likely damage the device. Voltage on any other pin with respect to VSS........................... -0.3V to (VDD + 0.3V) ELM327QSJ Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com 4 of 8 ELM327 Electrical Characteristics All values are for operation at 25°C and a 5V supply, unless otherwise noted. For further information, refer to note 1 below. Characteristic Minimum Typical Supply voltage, VDD 4.2 5.0 VDD rate of rise 0.05 Average current, IDD normal low power Input logic levels Schmitt trigger input thresholds Maximum Units 5.5 V V/ms 12 mA 0.15 mA low VSS 0.8 V high 3.0 VDD V 4.0 V rising falling 2.9 see note 2 ELM327 device only - does not include any load currents Pins 5, 6, 7, and 24 only Pins 1, 11, 12, 13, 15 and 18 only 1.5 V Output low voltage 0.3 V current (sink) = 10 mA Output high voltage 4.4 V current (source) = 10 mA Brown-out reset voltage 1.0 Conditions 2.65 A/D conversion time 2.79 9 Pin 18 wake pulse duration 128 IgnMon debounce time 50 2.93 V msec AT RV to beginning of response µsec to wake from Low Power mode 65 msec AT LP to PwrCtrl output time 1.0 sec LP ALERT to PwrCtrl output time 2.0 sec Reset time 800 msec 2 msec AT Z AT WS Measured from the end of the command to the start of the ID message (ELM327 v2.1) Notes: 1. This integrated circuit is based on Microchip Technology Inc.’s PIC18F2480 device. For more detailed device specifications, and possibly clarification of those given, please refer to the Microchip documentation (available at www.microchip.com). 2. This spec must be met in order to ensure that a correct power on reset occurs. It is quite easily achieved using most common types of supplies, but may be violated if one uses a slowly varying supply voltage, as may be obtained through direct connection to solar cells or some charge pump circuits. ELM327QSJ Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com 5 of 8 ELM327 AT Command Summary General Commands OBD Commands <CR> repeat the last command AL Allow Long (>7 byte) messages BRD hh try Baud Rate Divisor hh AMC display Activity Monitor Count BRT hh set Baud Rate Timeout AMT hh set the Activity Mon Timeout to hh D set all to Defaults AR Automatically Receive E0, E1 Echo off, or on* AT0, 1, 2 Adaptive Timing off, auto1*, auto2 FE Forget Events BD perform a Buffer Dump I print the version ID BI Bypass the Initialization sequence L0, L1 Linefeeds off, or on DP Describe the current Protocol LP go to Low Power mode DPN Describe the Protocol by Number M0, M1 Memory off, or on H0, H1 Headers off*, or on RD Read the stored Data MA Monitor All SD hh Save Data byte hh MR hh Monitor for Receiver = hh WS Warm Start (quick software reset) MT hh Monitor for Transmitter = hh Z reset all NL Normal Length messages* @1 display the device description PC Protocol Close @2 display the device identifier R0, R1 Responses off, or on* RA hh set the Receive Address to hh S0, S1 printing of Spaces off, or on* PP xx OFF disable Prog Parameter xx SH xyz Set Header to xyz PP FF OFF all Prog Parameters disabled SH xxyyzz Set Header to xxyyzz PP xx ON enable Prog Parameter xx SH wwxxyyzz Set Header to wwxxyyzz PP FF ON all Prog Parameters enabled SP h Set Protocol to h and save it PP xx SV yy for PP xx, Set the Value to yy SP Ah Set Protocol to Auto, h and save it PPS SP 00 Erase stored protocol SR hh Set the Receive address to hh SS use Standard Search order (J1978) @3 cccccccccccc store the @2 identifier Programmable Parameter Commands print a PP Summary Voltage Reading Commands ST hh Set Timeout to hh x 4 msec CV dddd Calibrate the Voltage to dd.dd volts TA hh set Tester Address to hh CV 0000 restore CV value to factory setting TP h Try Protocol h RV Read the input Voltage TP Ah Try Protocol h with Auto search Other IGN ELM327QSJ read the IgnMon input level Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com 6 of 8 ELM327 AT Command Summary (continued) J1850 Specific Commands (protocols 1 and 2) IFR0, 1, 2 IFRs off, auto*, or on IFR H, S IFR value from Header* or Source ISO Specific Commands (protocols 3 to 5) FI perform a Fast Initiation IB 10 set the ISO Baud rate to 10400* IB 48 set the ISO Baud rate to 4800 IB 96 set the ISO Baud rate to 9600 IIA hh set ISO (slow) Init Address to hh KW display the Key Words CAN Specific Commands (continued) D0, D1 display of the DLC off*, or on FC SM h Flow Control, Set the Mode to h FC SH hhh FC, Set the Header to hhh FC SH hhhhhhhh Set the Header to hhhhhhhh FC SD [1 - 5 bytes] FC, Set Data to [...] PB xx yy Protocol B options and baud rate RTR send an RTR message V0, V1 use of Variable DLC off*, or on J1939 CAN Specific Commands (protocols A to C) KW0, KW1 Key Word checking off, or on* DM1 monitor for DM1 messages SI perform a Slow (5 baud) Initiation JE use J1939 Elm data format* SW hh Set Wakeup interval to hh x 20 msec JHF0, JHF1 Header Formatting off, or on* SW 00 Stop sending Wakeup messages JS use J1939 SAE data format JTM1 set Timer Multiplier to 1* JTM5 set Timer Multiplier to 5 MP hhhh Monitor for PGN 0hhhh WM [1 - 6 bytes] set the Wakeup Message CAN Specific Commands (protocols 6 to C) CEA turn off CAN Extended Addressing CEA hh use CAN Extended Address hh CAF0, CAF1 Automatic Formatting off, or on* CF hhh set the ID Filter to hhh CF hhhhhhhh set the ID Filter to hhhhhhhh CFC0, CFC1 Flow Controls off, or on* CM hhh set the ID Mask to hhh CM hhhhhhhh set the ID Mask to hhhhhhhh CP hh set CAN Priority to hh (29 bit) CRA reset the Receive Address filters CRA hhh set CAN Receive Address to hhh CRA hhhhhhhh set the Rx Address to hhhhhhhh CS show the CAN Status counts CSM0, CSM1 Silent Monitoring off, or on* CTM1 set Timer Multiplier to 1* CTM5 set Timer Multiplier to 5 ELM327QSJ MP hhhh n “ “ and get n messages MP hhhhhh Monitor for PGN hhhhhh MP hhhhhh n Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com “ “ and get n messages 7 of 8 ELM327 Outline Diagrams The diagrams at the right show the two package styles that the ELM327 is available in. The first shows our ELM327P product in what is commonly called a ‘300 mil skinny DIP package’. It is used for through hole applications. The ELM327SM package shown at right is also sometimes referred to as 300 mil, and is often called an SOIC package. We have chosen to simply refer to it as an SM (surface mount) package. The drawings shown here provide the basic dimensions for these ICs only. Please refer to the following Microchip Technology Inc. documentation for more detailed information: Package Drawings and Dimensions Specification, (document name en012702.pdf - 7.5MB). Go to www.microchip.com, select ‘Design Support’ then ‘Documentation’ then ‘Packaging Specifications’, or go directly to www.microchip.com/packaging PIC18F2480/2580/4480/4580 Data Sheet, (document name 39637d.pdf - 8.0MB). Go to www.microchip.com, select ‘Design Support’ then ‘Documentation’ then ‘Data Sheets, and search for 18F2480. ELM327P 2.54 7.24 max 10.92 ELM327SM 1.27 7.50 10.30 Note: all dimensions shown are in mm. Ordering Information ELM327 integrated circuits are 28 pin devices, available in either a 300 mil wide plastic (‘skinny’) DIP format or in a 300 mil (7.50 mm body) SOIC surface mount type of package. We do not offer an option for QFN packages. To order, add the appropriate suffix to the part number: 300 mil 28 pin Plastic DIP..............................ELM327P 300 mil 28 pin SOIC....................................ELM327SM ELM327 is a registered trademark of Elm Electronics Inc. All rights reserved. Copyright 2005 to 2014 by Elm Electronics Inc. Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve reliability, function, or design. ELM327QSJ Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com 8 of 8