ELM329LP datasheet(45/87 Pages) ELM

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ELM329L

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ELM329L DSA

Elm Electronics – Circuits for the Hobbyist

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Restoring Order

There may be times when it seems the ELM329 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 ELM329 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 ELM329 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 for 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. If you have been experimenting with

CAN filters and are suddenly seeing ‘NO DATA’

responses, this can usually be fixed by resetting the

filters. Simply send:

>AT CRA

and the filter and mask will be reset to the default

values.

If you problem is more involved than this, then all

of the settings can be reset by sending the ‘set to

Defaults’ command:

>AT D

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 ELM329 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 ELM329. 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 ELM329, 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

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 system reset:

>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 65 and 66) for

more details.

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