ELM329LP datasheet(4/87 Pages) ELM

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ELM329L

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

Pin Descriptions

4 of 87

MCLR (pin 1)

A momentary (>2µsec) logic low applied to this input

will reset the ELM329. 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 VDD volt

signal that is applied to it. The value measured is

scaled by a factor of 5.7 if VDD is >4V, and by a

factor of 11 if VDD is <4V. The scaling is appropriate

for use with 47K

Ω/10KΩ and 47KΩ/4.7KΩ resistor

dividers, respectively. The measured voltage is

displayed using the AT RV command.

Care must be taken to prevent the voltage from

going outside of the supply levels of the ELM329, or

damage may occur. If it is not used, this pin should

be tied to either VDD or VSS.

Active LED (pin 3)

This output pin is normally at a high level, and is

driven to a low level when the ELM329 has

determined that it has found a valid (active) protocol.

The output is suitable for directly driving efficient

LEDs through a current limiting resistor, or for

interfacing to other logic circuits. If unused, this pin

may be left open-circuited.

Note that the behaviour of this pin when the ELM329

is in the low power mode may be modified by the

logic level at pin 11, or with PP 0F, bit 4. For the

ELM329L, the total current into or from pin 3 must

not exceed 2 mA.

Control (pin 4)

The level at this output may be directly controlled

through AT commands. After any reset (powerup,

AT Z, etc.), the output reverts to a low level.

Pin 4 may also be used to provide an output signal

that follows the internal CAN monitor output, by

setting bit 0 of PP 0F to 1. For the ELM329L, the

total current into or from pin 4 must not exceed 2

mA.

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.

Filter Cap (pin 6)

The ELM329L requires that a 10µF filter capacitor be

connected between pin 6 and VSS. The capacitor

should be a low ESR (<5

Ω) ceramic or tantalum

type.

The ELM329 uses pin 6 for setting the initial baud

rate after power on. Since this option is not available

with the ELM329L, it defaults to an initial baud rate

of 38400 bps. If you require 9600 bps, you must set

PP 0C to 00.

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

ELM329 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 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 from each of these pins to circuit common

(Vss).

When laying out a printed circuit board, you may

wish to consider placing a guard ring around the

oscillator crystal, pins, and capacitors, to provide a

little isolation between them and the other signals

(particularly the pin 11 CAN input).

Note that this device has not been configured for

operation with an external oscillator, and 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.

CAN Monitor (pin 11)

This input serves two functions. If a CAN signal is

detected at this pin, the ELM329 assumes that you

ELM329L DSA

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