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Elm 327 Manual

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Restoring Order
There may be times when it seems the ELM327 is
out of control, and you will need to know how to
restore order. Before we continue to discuss modifying
too many parameters, this seems to be a good point to
discuss how to ‘get back to the start’. Perhaps you
have told the ELM327 to monitor all data, and there
are screens and screens of data flying by. Perhaps the
IC is now responding with ‘NO DATA’ when it did work
previously. This is when a few tips may help.
The ELM327 can always be interrupted from a
task by a single keystroke from the keyboard. As part
of its normal operation, checks are made for received
characters and if found, the IC will stop what it is doing
at the next opportunity. Often this means that it will
continue to send the information on the current line,
then stop, print a prompt character, and wait for your
input. The stopping may not always seem immediate if
the RS232 send buffer is almost full, though – you will
not actually see the prompt character until the buffer
has emptied, and your terminal program has finished
printing what it has received.
There are times when the problems seem more
serious and you don’t remember just what you did to
make them so bad. Perhaps you have ‘adjusted’ some
of the timers, then experimented with the CAN filter, or
perhaps tried to see what happens if the header bytes
are changed. All of these can be reset by sending the
‘set to Defaults’ AT Command:
>AT D
OK
This will often be sufficient to restore order, but it
can occasionally bring unexpected results. One such
surprise will occur if you are connected to a vehicle
using one protocol, but the saved (default) protocol is
a different one. In this case, the ELM327 will close the
current session and then change the protocol to the
default one, exactly as instructed.
If the AT D does not bring the expected results, it
may be necessary to do something more drastic - like
resetting the entire IC. There are a few ways that this
can be performed with the ELM327. One way is to
simply remove the power and then reapply it. Another
way that acts exactly the same way as a power off and
then on is to send the full reset command:
>AT Z
It takes approximately one second for the IC to
perform this reset, initialize everything and then test
the four status LEDs in sequence. A much quicker
option is available with the ELM327, however, if the
led test is not required – the ‘Warm Start’ command:
>AT WS
The AT WS command performs a software reset,
restoring exactly the same items as the AT Z does, but
it omits the LED test, making it considerably faster.
Also, it does not affect any baud rates that have been
set with the AT BRD command (which AT Z does), so
is essential if you are modifying the RS232 baud rates
with software.
Any of the above methods should be effective in
restoring order while experimenting. There is always
the chance that you may have changed a
Programmable Parameter, however, and are still
having problems with your system. In this case, you
may want to simply turn off all of the Programmable
Parameters (which forces them to their default values).
To do so, send the command:
>AT PP FF OFF
which should disable all of the changes that you have
made. Since some of the Programmable Parameters
are only read during a system reset, you may have to
follow this command with a reset command:
>AT Z
after which, you can start over with what is essentially
a device with ‘factory settings’. There may be times
when even this command is not recognized, however.
If that is the case, you will need to use the hardware
method of turning the PPs off. See the section on
‘Programmable Parameters’ (pages 68 and 69) for
more details.
49 of 94ELM327DSJ Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
ELM327
… 49 …


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