ELM327
Power Control (continued)
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, and can be
changed at any time with the AT AMT command.
Setting the Activity Monitor Timeout to 00 blocks all the
Activity Monitor outputs.
The final method to enter the low power mode is
by a low level appearing at the ignition monitor input
(pin 15 - IgnMon), when both b7 and b2 of PP 0E are
set to ‘1’, allowing it.
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
AT LP
command
1 sec
delay
Go to
Low Power
b7
input is
quiet
b0*
b4
RS232
detector
RS232 Rx
(pin 18)
5 min or 20 min
timer
flash OBD
Tx LED
not
monitoring
b5
b3
b7
1 min
remaining
print
ACT ALERT
2 sec
delay
all are
quiet
activity
monitor
OBD
inputs
b7
160 sec timer
(read with AT AMC)
1 sec
delay
b5*
not
sent a
message
monitoring
print
LP ALERT
>
Timeout setting
b3*
AMT ¹ 00
b4*
AMT
b7*
Notes
print
ACT ALERT
Bits with an asterisk (*) are for PP 0F.
All other bits are for PP 0E.
represents an AND gate
represents an OR gate
voltage
is low
IgnMon
(pin 15)
voltage
monitor
65 msec
debounce
b2
b7
Figure 6. Enabling the Low Power Mode
ELM327DSI
Elm Electronics – Circuits for the Hobbyist
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