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ELM329
ELM329DSC
Elm Electronics – Circuits for the Hobbyist
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AT Command Descriptions (continued)
adds the ability to set the number of messages that
should be fetched before the ELM329 automatically
stops monitoring and prints a prompt character. The
value ‘n’ may be any single hex digit.
MP hhhhhh
[ Monitor for PGN hhhhhh ]
This command is very similar to the MP hhhh
command, but it extends the number of bytes provided
by one, so that there is complete control over the PGN
definition (it does not make the assumption that the
Data Page bit is 0, as the MP hhhh command does).
This allows for future expansion, should additional
PGNs be defined with the Data Page bit set. Note that
internally, the filter and mask are set using the values
provided, but only the Data Page bit is relevant in the
mask - the other bits are ignored. If you need more
precise matching of the priority and EDP bits, you
might consider the AT CM and AT CF commands to
set the filter and mask, then use AT MA.
MP hhhhhh n
[ Monitor for PGN, get n messages ]
This is very similar to the previous command, but it
adds the ability to set the number of messages that
should be fetched before the ELM329 automatically
stops monitoring and prints a prompt character. The
value ‘n’ may be any single hex digit.
PB xx yy
[ set Protocol B parameters ]
This command allows you to change the protocol
B (USER1) options and baud rate without having to
change the associated Programmable Parameters.
This allows for quicker testing, and program control.
To use this feature, simply set xx to the value for
PP 2C (the formatting options), and yy to the value for
PP 2D (the baud rate divisor), and send this
command. The next time that the protocol is initialized
it will use these values.
For example, assume that you wish to try
monitoring a system that uses 11 bit CAN at
33.3 kbps. If you do not want any special formatting,
this means a value of 11000000 (C0 hex) for PP 2C,
while 33.3 is 500/15 so 15 decimal or 0F hex is
needed for PP 2D. Send these values to the ELM329
in one command:
>AT PB C0 0F
then monitor:
>AT MA
If you want to try another protocol (for example,
500 kbps J1939) then simply close the current protocol
and send another AT PB command:
>AT PC
OK
>AT PB 42 01
OK
>AT MA
Values passed in this way do not affect those that
are stored in the 2C and 2D Programmable
Parameters, and are lost if the ELM329 is reset. If you
want to make your settings persist over power cycles,
then you must store them in the Programmable
Parameter memory for one of the five USER protocols
(ie protocols B to F).
PC
[ Protocol Close ]
There may be occasions where it is desirable to
stop (deactivate) a protocol. Perhaps you are not using
the automatic protocol finding, and wish to manually
activate and deactivate protocols. Perhaps you wish to
stop the sending of idle (wakeup) messages, or have
another reason. The PC command is used in these
cases to force a protocol to close.
PP hh OFF
[ turn Prog Parameter hh OFF ]
This command disables Programmable Parameter
number hh. Any value assigned using the PP hh SV
command will no longer be used, and the factory
default setting will once again be in effect. The actual
time when the new value for this parameter becomes
effective is determined by its type. Refer to the
Programmable Parameter Summary section (page 65)
for more information on the types.
Note that ‘PP FF OFF’ is a special command that
disables all of the Programmable Parameters, as if you
had entered PP OFF for every possible one.
It is possible to alter some of the Programmable
Parameters so that it may become difficult, or even
impossible, to communicate with the ELM329. If this
occurs, there is a hardware means of resetting all of
the Programmable Parameters at once. Connect a
jumper from circuit common to pin 28, holding it there