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ELM323 Datasheet(PDF) 2 Page - ELM Electronics |
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ELM323 Datasheet(HTML) 2 Page - ELM Electronics |
2 / 19 page ELM323 Elm Electronics – Circuits for the Hobbyist < http://www.elmelectronics.com/ > Pin Descriptions 2 of 19 All rights reserved. Copyright 2001, 2003 Elm Electronics. 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. VDD (pin 1) 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 microprocessor, so an external reset signal is not required. Refer to the Electrical Characteristics section for further information. XT1 (pin 2) and XT2 (pin 3) A 3.579545 MHz NTSC television colourburst crystal is connected between these two pins. Crystal loading capacitors (typically 27pF) will also normally be connected between each of these pins and the circuit common (Vss). LFmode (pin 4) This input is used to select the default linefeed mode after a power-up or system reset. If it is at a high level, then by default messages sent by the ELM323 will be terminated with both a carriage return and a linefeed character. If it is at a low level, lines will be terminated by a carriage return only. This behavior can always be modified by issuing AT L0 or AT L1 commands (see the section on AT Commands). RS232Rx (pin5) A computer’s RS232 transmit signal can be directly connected to this pin from the RS232 line as long as a current limiting resistor (typically about 47K Ω) is installed in series. (Internal protection diodes will pass the resistor current safely to the supply connections, protecting the ELM323.) Internal signal inversion and Schmitt trigger waveshaping provide the necessary signal conditioning. RS232Tx (pin 6) This is the RS232 transmit or data output pin. The signal level is compatible with most interface ICs, and there is sufficient current drive to allow interfacing using only a PNP transistor, if desired. LED Drive Outputs (pins 7, 8, 9, and 10) These four pins are driven to low levels when the ELM323 is transmitting or receiving RS232 or OBD data. Otherwise, they are at a high level. Current capability is suitable for directly driving most LEDs through current limiting resistors. If unused, these pins should be left open-circuited. OBDIn (pin11) The OBD data is input to this pin, with a high logic level representing the active state of the OBD K line. No Schmitt trigger input is provided, so the OBD signal should be buffered to minimize transition times for the internal CMOS circuitry. OBDL (pin 12) and OBDK (pin 13) These are the active high output signals which are used to drive the OBD bus, using external NPN transistors. Data transfer normally occurs only by the K line, but the standards require that the L line be implemented as well in order to properly initialize the bus. See the Example Applications section for more details. VSS (pin 14) Circuit common is connected to this pin. This is the most negative point in the circuit. ELM323DSC Ordering Information These integrated circuits are available in either the 300 mil plastic DIP format, or in the 150 mil SOIC surface mount type of package. To order, add the appropriate suffix to the part number: 300 mil Plastic DIP...................................ELM323P 150 mil SOIC........................................ ELM323SM |
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