ELM327LP Datasheet, PDF (29/94 Pages) ELM Electronics – Automatically searches for protocols

ELM327L
AT Command Descriptions (continued)
command above, except that if the protocol that is tried
should fail to initialize, the ELM327 will then
automatically sequence through the other protocols,
attempting to connect to one of them.
V0 and V1
[ Variable data lengths off or on ]
Many CAN protocols (ie ISO 15765-4) expect to
send eight data bytes at all times. The V0 and V1
commands may be used to override this behaviour (for
any CAN protocol) should you wish.
Choosing V1 will cause the current CAN protocol
to send variable data length messages, just as bit 6 of
PP 2C and PP 2E do for protocols B and C. It does not
matter what the protocol should be doing - V1 will
override that. This allows experimenting with variable
data length messages on demand.
If you select V0 (the default setting), the forced
sending of variable length CAN messages is turned
off. The format of the sent messages reverts to the
protocol’s settings.
WM [1 to 6 bytes]
[ set Wakeup Message to… ]
This command allows the user to override the
default settings for the wakeup messages (sometimes
known as the ‘periodic idle’ messages). Simply provide
the message that you wish to have sent (typically three
header bytes and one to three data bytes), and the
ELM327 will add the checksum and send them as
required, at the rate determined by the AT SW setting.
Default settings will send the bytes 68 6A F1 01 00
for ISO 9141, and C1 33 F1 3E for KWP.
WS
[ Warm Start ]
This command causes the ELM327 to perform a
complete reset. It is very similar to the AT Z command,
but does not include the power on LED test. Users
may find this a convenient way to quickly ‘start over’
without having the extra delay of the AT Z command.
If using variable RS232 baud rates (ie AT BRD
commands), it is preferred that you reset the IC using
this command rather than AT Z, as AT WS will not
affect the chosen RS232 baud rate.
Z
[ reset all ]
This command causes the chip to perform a
complete reset as if power were cycled off and then on
again. All settings are returned to their default values,
and the chip will be put into the idle state, waiting for
characters on the RS232 bus. Note that any baud rate
that was set with the AT BRD command will be lost,
and the ELM327 will return to the default baud rate
setting.
@1
[ display the device description ]
This command displays the device description
string. The default text is ‘OBDII to RS232 Interpreter’.
@2
[ display the device identifier ]
A device identifier string that was recorded with
the @3 command is displayed with the @2 command.
All 12 characters and a terminating carriage return will
be sent in response, if they have been defined. If no
identifier has been set, the @2 command returns an
error response (‘?’). The identifier may be useful for
storing product codes, production dates, serial
numbers, or other such codes.
See the ‘Programming Serial Numbers’ section for
more information.
@3 cccccccccccc
[ store the device identifier ]
This command is used to set the device identifier
code. Exactly 12 characters must be sent, and once
written to memory, they can not be changed (ie you
may only use the @3 command one time). The
characters sent must be printable (ascii character
values 0x21 to 0x5F inclusive).
If you are developing software to write device
identifiers, you may be interested in the ELM328 IC, as
it allows multiple writes using the @3 command (but it
can not send OBD messages).
ELM327L DSA
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