ELM325
AT Command Descriptions (continued)
F1 hh hh hh hh hh
[ set Filter 1 to… ]
(0x0D). Users will generally wish to have this option on
if using a terminal program, but off if using a custom
computer interface (as the extra characters transmitted
will only serve to slow the communications down). The
default setting is L1 (linefeeds on).
Filter F1 can be used to selectively receive only
the messages that contain matching bytes in the first
five byte positions. Simply set the values for the five
bytes (ten nibbles) with this command and the
ELM325 will make the internal adjustments for you. If
there is a nibble that can have any value, then use the
letter ‘X’ to define it. See the Receive Filtering section
for more details.
MA
[ Monitor All messages ]
This command places the ELM325 into a bus
monitoring mode, in which it continually monitors for
(and displays) all messages that it sees. If the F1 and
F2 filters have not been set, then all messages on the
J1708 bus will be displayed.
Often, it is not desirable to display everything that
is being transmitted on the system. If you wish to
reduce the amount of information displayed, simply set
the F1 and/or F2 filters to the values that you wish to
see. Then, with AT MA, the ELM325 will display all
messages that meet that criteria.
F2 hh hh hh hh hh
[ set Filter 2 to… ]
Filter F2 can be used to selectively receive only
the messages that contain matching bytes in the first
five byte positions. Simply set the values for the five
bytes (ten nibbles) with this command and the
ELM325 will make the internal adjustments for you. If
there is a nibble that can have any value, then use the
letter ‘X’ to define it. See the Receive Filtering section
for more details.
MM hh
[ Monitor for MID hh ]
GM
[ Get Message ]
The AT MM command is similar to the AT MA
command except that it also filters for only messages
that match the MID provided. That is, the AT MM
command is effectively an extra filter that can be
applied to incoming messages.
Occasionally, you may wish to set the receive filter
for a particular message and ‘get’ it from the data
stream. The AT GM command may be used to do so.
This command is very similar to AT MA with the
F1/F2 filters set, except that it respects the AT ST
timeout value. That is, if no message is received in the
ST time, the ELM325 will return with a NO DATA
message, and if multiple messages are received within
that time, they will all be displayed. Note that F1 and/or
F2 must be set prior to using AT GM.
MP hh
[ Monitor for PID hh ]
The AT MP command is very similar to the AT MM
command except that it only allows messages with the
provided PID value in the second byte position. Again,
the F1 and/or F2 filters may be used to further refine
the data that is shown.
GO
[ Get One message ]
MP 01hh
[ Monitor for page 2 PID hh ]
This command performs exactly as the AT GM
command, except that it only gets one response and
then returns immediately to the prompt.
This command is identical to the previous
command except that it filters for page 2 PIDs (that is,
for PIDs of value 0100 to 01FF). Again, F1 and F2
filters can also be used with this command.
I
[ Identify yourself ]
As an aside, this command actually monitors for
0xFF in the second byte position, and for the hh value
in the third byte position (which is the way that page 2
PIDs are defined in the SAE J1587 standard).
Issuing this command causes the chip to identify
itself, by printing the startup product ID string (currently
‘ELM325 v1.0’). Software can use this to determine
exactly which integrated circuit it is talking to, without
having to reset the IC.
R0 and R1
[ Responses off or on* ]
L0 and L1
[ Linefeeds off or on* ]
These commands control whether the ELM325 will
look for a response from the vehicle, after a message
has been sent. If responses have been turned off (with
This option controls the sending of linefeed
characters (0x0A) after each carriage return character
ELM325DSA
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