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silently (ie you may want it to generate ACK bits, etc.),
and this is what the CSM command is for. CSM1 turns
silent monitoring on (no ACKs), CSM0 turns it off. The
default value is CSM1, but it may be changed with
PP 21.
CV dddd [ Calibrate the Voltage to dd.dd volts ]
The voltage reading that the ELM329 shows for an
AT RV request can be calibrated with this command.
The argument (‘dddd’) must always be provided as 4
digits, with no decimal point (it assumes that the
decimal place is between the second and the third
digits).
To use this feature, simply use an accurate meter
to read the actual input voltage, then use the CV
command to change the internal calibration (scaling)
factor. For example, if the ELM329 shows the voltage
as 12.2V while you measure 11.99 volts, then send
AT CV 1199 and the ELM329 will recalibrate itself for
that voltage (it will actually read 12.0V due to digit
roundoff). See page 26 for some more information on
how to read voltages and perform the calibration.
CV 0000 [ restore the factory Calibration Value ]
If you are experimenting with the CV dddd
command but do not have an accurate voltmeter as a
reference, you may soon get into trouble. If this
happens, you can always send AT CV 0000 to restore
the ELM329 to the original calibration value.
D [ set all to Defaults ]
This command is used to set the options to their
default (or factory) settings, as when power is first
applied. The last stored protocol will be retrieved from
memory, and will become the current setting (possibly
closing a protocol that was active). Any settings that
the user had made for custom headers, filters, or
masks will be returned to their default values, and all
timer settings will also be restored to their defaults.
D0 and D1 [ display of DLC off or on ]
Standard CAN (ISO 15765-4) OBD requires that
all messages have 8 data bytes, so displaying the
number of data bytes (the DLC) is not normally very
useful. When experimenting with other protocols,
however, it may be useful to be able to see what the
data lengths are. The D0 and D1 commands control
the display of the DLC digit (the headers must also be
on in order to see this digit). When displayed, the
single DLC digit will appear between the ID (header)
bytes and the data bytes. The default setting is
determined by PP 29.
DM1 [ monitor for DM1s ]
The SAE J1939 Protocol broadcasts trouble codes
periodically, by way of the Diagnostic Mode 1 (DM1)
messages. This command sets the ELM329 to
continually monitor for this type of message for you,
even following multi-segment transport protocols if
required. Note that a combination of masks and filters
could be set to provide a similar output, but they would
not allow multiline messages to be detected. The DM1
command adds the extra logic that is needed for
multiline messages.
This command is only available when a protocol
has been selected for J1939 formatting. It returns an
error if attempted under any other conditions.
DP [ Describe the current Protocol ]
The ELM329 automatically detects a vehicle’s
OBD protocol, but does not normally report what it is.
The DP command is a convenient means of asking
what protocol the IC is currently set to (even if it has
not yet ‘connected’ to the vehicle).
If a protocol is chosen and the automatic option is
also selected, AT DP will show the word 'AUTO' before
the protocol description. Note that the description
shows the actual protocol names, and the data rates, it
does not provide the numbers used by the protocol
setting commands (see DPN for this).
DPN [ Describe the Protocol by Number ]
This command is similar to the DP command, but
it returns a number which represents the current
protocol. If the automatic search function is also
enabled, the number will be preceded with the letter
‘A’. The number is the same one that is used with the
set protocol and test protocol commands (see page 32
for a list of them).
E0 and E1 [ Echo off or on ]
These commands control whether or not the
characters received on the RS232 port are echoed
(retransmitted) back to the host computer. Character
echo can be used to confirm that the characters sent
AT Command Descriptions (continued)
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