ELM327P datasheet(62/76 Pages) ELM

62 / 76 page

62 of 76

ELM327

ELM327DSH

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

Power Control

Often, the ELM327 is connected to a vehicle for

only a short time, so power consumption is not of great

concern. Occasionally, the ELM327 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 new power control features of the

ELM327 were introduced for this.

There are three ways in which the ELM327 can be

placed into the low power standby mode (shown

pictorially in Figure 6 below). None of the three will

work without having the master enable (ie bit 7 of

PP 0E) set to ‘1’, which it is by default.

The first method is with an AT command. You may

simply send:

>AT LP

and the IC will go to the low power mode after a one

second delay (which allows the controlling circuit a

little time to perform some housekeeping tasks).

At the end of the delay, all of the ELM327 outputs

go to their recessive/off state, the pin 3 control for the

J1850 voltage will go low, and the pin 16 control output

will reverse its state. The ELM327 will then reduce its

power level, and begin monitoring for inputs that would

cause a shift back to full power.

The next method allows automatic switching to the

low power mode when there has been no RS232 input

for a period of time - a good backup for your low power

strategy. To enable this method, both b7 and b5 of

PP 0E must be set to ‘1’. The time delay (either 5 or 20

minutes) is set by b4, and the printing of a warning is

enabled with b3. The warning is handy in some cases

– it is the activity alert message (‘ACT ALERT’) and is

sent 1 minute before the timer is about to time out.

When the timer does time out, you will see a low

power alert warning (‘LP ALERT’), and then 2 seconds

later, all of the outputs will change as described above

for the AT LP command.

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 method uses a short internal

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

Figure 6. Enabling the Low Power Mode

debounce

circuit

AT LP

command

IgnMon

(pin 15)

1 sec

delay

5 min or 20 min

time delay on pick up

(fast reset)

RS232 Rx

(pin 18)

idle (at prompt),

waiting for input

1 min

remaining

ACT ALERT

LP ALERT

Go to Low Power

• pin 16 = b6

• LEDs off

• pin 3 = 0V

• µP to low power

2 sec

delay

ELM327P Datasheet(PDF) 62 Page - ELM Electronics

ELM327P Datasheet(HTML) 62 Page - ELM Electronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76

Datasheet Download

Link URL