Manual Elm 327 (page 28 of 94) (English)

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ELM327

ELM327DSJ Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

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).

AT Command Descriptions (continued)

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