ELM327LSM datasheet(66/94 Pages) ELM

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ELM327L DSA

Elm Electronics – Circuits for the Hobbyist

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ELM327L

to cause the ELM327 to shift to Low Power operation,

if there is no OBD activity for some time. If you follow

the logic path, you will see that b7 and b5 of PP 0F

must both be ‘1’, as well as b7 of PP 0E in order to

allow this switch to occur. The default time that it

allows before switching is set by b4, unless you have

set a value with the AT AMT command. Setting the

Activity Monitor Timeout to 00 blocks all the Activity

Monitor outputs.

The final way to enter the low power mode is by a

low level appearing at the ignition monitor input

(pin 15), with both b2 and b7 of PP 0E set to ‘1’.

The ignition monitor logic inserts a short internal

delay (‘debounce’) to be sure that the low level seen is

a legitimate ‘key off’ and not just some noise. After it is

sure, the ELM327 will then send a low power alert

message (‘LP ALERT’), and 2 seconds later it will

switch to Low Power operation, just the same as was

Figure 6. Enabling the Low Power Mode

Power Control (continued)

OBD

inputs

AT LP

command

1 min

remaining

LP ALERT

Go to

Low Power

65 msec

debounce

IgnMon

(pin 15)

voltage

is low

RS232 Rx

(pin 18)

input is

quiet

all are

quiet

sent a

message

not

monitoring

b0*

flash OBD

Tx LED

activity

monitor

timer

≥

setting?

AMT

≠ 00

b3*

ACT ALERT

b5*

1 sec

delay

2 sec

delay

ACT ALERT

1 sec

delay

RS232

detector

not

monitoring

voltage

monitor

Notes

PP 0F bits are shown with an asterisk (*).

All other bits are for PP 0E.

represents an AND gate

represents an OR gate

5 min or 20 min

timer

(read with

AT AMC)

timer

Timeout setting

AMT value, if set

else

150 sec if b4*= 1

30 sec if b4*= 0

yes

b7*

ELM327LSM Datasheet(PDF) 66 Page - ELM Electronics

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