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results when a value of FF (decimal 255) is used. The
default setting provides a nominal delay of 2 seconds
between messages. The replies to these messages
are always ignored, and are not visible to the user.
Note that the value 00 (zero) is treated as a very
special case, and must be used with caution, as it will
stop all periodic messages. This way of stopping the
messages while keeping the rest of the protocol
functioning normally, is for experimenters, and is not
intended to be used regularly. Issuing AT SW 00 will
not change a prior setting for the time between
wakeup messages, if the protocol is reinitialised.
TA hh [ set the Tester Address to hh ]
This command is used to change the current
tester (ie. scan tool) address that is used in the
headers, periodic messages, filters, etc. The ELM329
normally uses the value that is stored in PP 06 for this,
but the TA command allows you to temporarily
override that value.
Sending AT TA will affect all protocols, including
J1939. This provides a convenient means to change
the J1939 address from the default value of F9,
without affecting other settings.
Although this command may appear to work ‘on
the fly’, it is not recommended that you try to change
this address after a protocol is active, as the results
may be unpredictable.
TM0, TM1, TM2, TM3 [ set the Transceiver Mode… ]
This command is used to control the voltage levels
at pins 21 (M1) and 22 (M0), and are typically used
with single wire CAN transceivers. The four modes
are:
0: sleep (M1=0, M0=0)
1: high speed (M1=0, M0=1)
2: high voltage wakeup (M1=1, M0=0)
3: normal (M1=1, M0=1)
Note that during low power operation, the M0 and
M1 pins will maintain the setting that they had prior to
going to low power mode. The previous version of this
IC (v1.0) automatically set both pins to a low level,
which is a ‘sleep’ output. As the ELM329 ‘wakes up’
from low power operation, the level at M0 and M1 will
be set according to PP 20. For more details on how to
use these commands, see page 59.
TP h [ Try Protocol h ]
This command is identical to the SP command,
except that the protocol that you select is not
immediately saved in internal memory, so does not
change the default setting. Note that if the memory
function is enabled (AT M1), and this new protocol that
you are trying is found to be valid, that protocol will
then be stored in memory as the new default.
TP Ah [ Try Protocol h with Auto ]
This command is very similar to the AT TP
command above, except that if the protocol that is tried
should fail to initialize, the ELM329 will then
automatically sequence through the other protocols,
attempting to connect to one of them.
V0 and V1 [ Variable data lengths off or on ]
These commands modify the current CAN protocol
settings to allow the sending of variable data length
messages (just as setting bit 6 of the CAN Options PP
does for protocols B to F). This allows experimenting
with variable data length messages for any of the CAN
protocols, without having to change the Programmable
Parameter. The V1 command will always override any
protocol setting, and force a variable data length
message. The default setting is V0, providing data
lengths as determined by the protocol.
WD [1 to 8 bytes] [ set Wakeup Data to… ]
This command allows you to define the data bytes
that will be sent in the wakeup (CAN periodic)
message. Any number of bytes from 1 to 8 may be
defined, and will be sent exactly as provided. That is,
no formatting will be applied, no filler bytes will be
added, and the data length code will be set to the
number of data bytes provided (even if the protocol
expects 8 bytes). If you do need to send 8 bytes, you
will need to provide 8 bytes. The default setting for WD
is 01 3E 00 00 00 00 00 00.
WH xyz [ set Wakeup Header to… ]
The AT WH xyz command accepts a three digit
argument, takes only the right-most 11 bits from that,
and uses that for the 11 bit Wakeup Header. You may
define a wakeup message to use an 11 bit ID even if
the current protocol uses 29 bit IDs. The last assigned
wakeup header (11 or 29 bit) determines whether the
AT Command Descriptions (continued)
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