Bedienungsanleitung Elm 327 (Seite 68 von 94) (Englisch)

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Programmable Parameters

The ELM327 contains several memory locations

that retain their data even after power is turned off.

Every time the IC is reset, these locations are read

and used to change the default settings for such things

as whether to display the headers, or how often to

send ‘wakeup’ messages. Because they define the

operation of the ELM327, we refer to these memory

locations as the Programmable Parameters.

All of the Programmable Parameters are easily

altered at any time using a few simple commands.

These commands are standard AT Commands, with

one exception: each one requires a two-step process

to complete. This extra step provides some security

against random inputs that might otherwise cause

changes.

As an example of how to change a Programmable

Parameter, consider PP 01 (shown on page 69) which

sets the default state for the AT H command. If you are

constantly powering your ELM327 and then using

AT H1 to turn the headers on, you may want to change

the default setting, so that the headers are always on

by default. To do this, simply set the value of PP 01 to

00:

>AT PP 01 SV 00

This changes the value associated with PP 01, but

does not yet enable it. To make the change effective,

you must also type:

>AT PP 01 ON

At this point, you have changed the default setting

for AT H1/H0, but you have not changed the current

AT H1/H0 setting. From the ‘Type’ column in the table

on page 69, you can see that PP 01 is a type ‘D’

parameter, so the change only becomes effective the

next time that defaults are restored. This could be from

a reset, a power off/on, or possibly an AT D command.

If you send the command AT D, then you should find

that the headers are now displayed by default.

As there are many Programmable Parameters that

you can alter, it might occasionally be difficult to know

what changes you have made to them. To help with

that, the ELM327 provides a Programmable Parameter

Summary (PPS) command. This command simply

prints a list of the entire range of PPs (whether

currently supported or not), their current value, and

whether they are on/enabled (N), or off/disabled (F).

For a version 2.1 ELM327, with only the headers

enabled (PP 01, as discussed above), the summary

table would look like:

>AT PPS

00:FF F 01:00 N 02:FF F 03:32 F

04:01 F 05:FF F 06:F1 F 07:09 F

08:FF F 09:00 F 0A:0A F 0B:FF F

0C:68 F 0D:0D F 0E:9A F 0F:D5 F

10:0D F 11:00 F 12:FF F 13:55 F

14:50 F 15:0A F 16:FF F 17:6D F

18:31 F 19:31 F 1A:FF F 1B:FF F

1C:03 F 1D:0F F 1E:4A F 1F:FF F

20:FF F 21:FF F 22:FF F 23:FF F

24:00 F 25:00 F 26:00 F 27:FF F

28:FF F 29:FF F 2A:3C F 2B:02 F

2C:E0 F 2D:04 F 2E:80 F 2F:0A F

You can see that PP 01 now shows a value of 00,

and it is enabled (oN), while the others are all off.

Another example shows how you might change

the CAN filler byte. Some systems use ‘AA’ as the

value to send for unused CAN data bytes, while the

ELM327 uses ‘00’ by default. To change the ELM327

in order to have it send AAs instead, simply change

PP 26:

>AT PP 26 SV AA

>AT PP 26 ON

Again, PP 26 is of type ‘D’, so the above change

will not actually take effect until the defaults are

restored, whether it be by an AT D command, or by

resetting the ELM327.

The Programmable Parameters are a great way to

customize your ELM327 for your own use, but you

should do so with caution if using commercial

software. Most software expects an ELM327 to

respond in certain ways to commands, and may be

confused if the carriage return character has been

redefined, or if the CAN response shows a data length

code digit, for example. If you make changes, it might

be best to make small changes and then see the effect

of each, so that it is easier to retrace your steps and

‘undo’ what you have done, should you have to. If you

get in too deeply, don’t forget the ‘all off’ command:

>AT PP FF OFF

No matter what software you use, you might get

into more serious trouble, should you change the baud

ELM327

68 of 94ELM327DSJ Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

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