ELM329
AT Command Descriptions (continued)
CV 0000
[ restore the factory Calibration Value ]
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).
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.
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 31
for a list of them).
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.
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
to the ELM329 were received correctly. The default is
E1 (or echo on).
FC SD [1-8 bytes]
[ Flow Control Set Data to… ]
The data bytes that are sent in a CAN Flow
Control message may be defined with this command.
One to eight data bytes may be specified, with the
remainder of the bytes in the message being
automatically set to the default CAN filler byte, if more
bytes are required by the protocol. Note that no
formatting bytes (PCI, etc.) are added by this
command - the data is used exactly as provided,
except for the filler bytes. AT FC SD is used with Flow
Control modes 1 and 2.
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.
FC SH xyz
[ Flow Control Set Header to… ]
This command is only available when a protocol
has been selected for J1939 formatting. It returns an
error if attempted under any other conditions.
The header (or more properly ‘CAN ID’) bytes
used for CAN Flow Control messages can be set using
this command. Only the right-most 11 bits of those
provided will be used - the most significant bit is
always ignored. This command only affects Flow
Control mode 1.
DP
[ Describe the current Protocol ]
The ELM329 automatically detects a vehicle’s
ELM329DSB
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