ELM329LP datasheet(5/87 Pages) ELM

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ELM329L DSA

wish it to monitor that signal, and possibly control the

low power operation based on it.

If no CAN signal is detected, the ELM329 assumes

that you are using this pin to control the behaviour of

the Active LED output when the IC is in the low

power mode (as it did for v1.0 ICs). In this mode, if

pin 11 is at a high level when low power operation

begins, the Active LED output will flash for about

16 msec every 4 seconds. If the input is at a low

level

when

low

power

operation

begins,

the

Active LED output will be off (high) when in low

power mode. If a CAN signal was detected on pin

11, the operation of the Active LED during low power

is determined by PP 0F, bit 4.

Monitoring for a CAN signal (ie. transitions at this

input pin) is a continuous background process that

can not be disabled.

In1 and In2 (pins 12 and 13)

These two inputs may be used for the monitoring of

logic level signals. Simple AT commands may be

used to read the level at either pin. No special

amplification is required, as the inputs have Schmitt

trigger wave shaping.

PwrCtrl (pin 14)

This output provides a level that is the inverse of that

of the PwrCtrl output (pin 16). If the low power mode

is disabled (ie if bit 7 of PP 0E is set to ‘0’), this

output still provides the inverse of the level set by

PP 0E b6. To provide a ‘soft start’ feature, pin 14 will

always change state 50 msec before pin 16.

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 set to ‘1’, this pin

will act as an Ignition Monitor. This will result in a

switch to the low power mode of operation, if the

input goes to a low level, as would happen if the

vehicle’s

ignition

were

turned

off.

internal

‘debounce’ timer is used to ensure that the ELM329

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 ELM329 will return to

normal operation. A low to high transition at pin 15

will always 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 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 if connected to

ignition positive, 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 ELM329 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 ELM329 switches to

the low power mode of operation. This output is

typically used to control enable inputs, but may also

be used for relay circuits, etc. with suitable buffering.

The discussion on page 80 (‘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 ELM329 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, pin 16 provides the PwrCtrl 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.

Pin Descriptions (continued)

ELM329L

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