ELM329LP datasheet(6/87 Pages) ELM

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ELM329L DSA

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ELM329L

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 microprocessor, so an external

reset signal is not required. Refer to the Electrical

Characteristics section for further information.

M1 (pin 21) and M0 (pin 22)

These two output pins are provided for use with CAN

transceiver ICs, as are typically used for Single Wire

CAN applications. The ELM329 will set both outputs

to a high level (‘Normal’) after startup, but the level at

these pins may be changed at any time with the

AT TM commands, and the level after powerup may

be set with PP20.

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

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 ELM329 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 66 for more

details.

Pin Descriptions (continued)

Unused Pins

When people only want to implement a portion of what the ELM329L 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 always be terminated. The ELM329L is a CMOS integrated circuit that can not have any inputs

left floating (or you might damage the IC). Connect unused inputs as follows:

Level

The inputs that are shown with an asterisk (*) may be connected to either a High (VDD) or a Low (VSS) level.

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