ELM329
Low Power Mode
Often, the ELM329 is connected to a vehicle for
that the master enable bit (bit 7 of PP 0E) be set to ‘1’
for them to function (which it is by default).
The first method is with an AT command. Simply
send ‘AT LP’ at the prompt:
only a short time, so power consumption is not of great
concern. Occasionally, the ELM329 may be connected
for longer times, however, possibly without the engine
running. For these applications, it is often desirable to
be able to put the circuit into a low power ‘standby’
state, and have it return to normal operation when
needed. The power control features of the ELM329 are
provided for this.
>AT LP
and the ELM329 will go to the low power mode after a
one second delay (which gives the controlling circuit a
little time to perform some housekeeping tasks).
When the ELM329 goes to the low power mode, it
first turns all five LED outputs off, then switches pin 14
There are four ways in which the ELM329 can be
placed into the low power standby mode (these are
shown pictorially in Figure 6 below). They all require
AT LP
command
1 sec
delay
Go to
Low Power
b7
input is
quiet
2 sec
delay
b6*
CAN Monitor
(pin 11)
activity
monitor
2 or 10 minute
delay
print
LP ALERT
b7*
1 min
remaining
b5*
not
monitoring
b7
print
ACT ALERT
input is
quiet
b4
RS232 Rx
(pin 18)
activity
monitor
5 or 20 minute
delay
b5
idle
(at prompt)
1 min
remaining
b3
b7
Note:
Bits with an asterisk (*) are for PP 0F.
All other bits are for PP 0E.
print
ACT ALERT
voltage
is low
voltage
monitor
IgnMon
(pin 15)
65 msec
debounce
b2
b7
Figure 6. Enabling the Low Power Mode
ELM329DSB
Elm Electronics – Circuits for the Hobbyist
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