ELM327P datasheet(16/51 Pages) ELM

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ELM327

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AT Commands (continued)

Setting the timer to a new value simply requires

using the ST command. For example, AT ST 19 will

give a setting of about 100 msec (19 in hex is 25 in

decimal). The ST timer is set to 32 by default (205

msec), but the default setting can be adjusted by

changing PP 03. Note that a value of 00 does not

result in 0 msec – it is a special value that sets the

timer to the default value.

When Adaptive Timing is enabled, the AT ST time

is modified by the actual measured response times,

however, the timer will never be set to a value that is

greater than the AT ST setting.

SW hh

[ Set Wakeup to hh ]

Once a data connection has been made, some

vehicles require that there be data flow every few

seconds, or the connection may time out and ‘go to

sleep.’

The

ELM327

will

automatically

generate

periodic ‘wakeup’ messages in order to maintain this

connection, whenever the user is not requesting any

data. (Currently, only protocols 3, 4, and 5 generate

these messages.) The replies to these messages are

always ignored, and are not visible to the user.

The time interval between these periodic ‘wakeup’

messages can be adjusted in 20 msec increments

using the AT SW hh command, where hh is any

hexadecimal value from 00 to FF. The maximum

possible time delay of just over 5 seconds thus occurs

when a value of FF (decimal 255) is used. The default

setting provides a nominal delay of 3 seconds between

messages.

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 is provided as it may

convenient

certain

circumstances.

Issuing

AT SW 00 will not change a prior setting for the time

between wakeup messages, should the protocol be re-

initialized.

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

initialize,

the

ELM327

will

then

automatically sequence through all of the protocols,

attempting to connect to one of them.

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 bytes that you wish to have sent (one to six of

them), and the ELM327 will then send them as

required, at the rate determined by the AT SW setting.

Note that you do not have to add a checksum byte to

the data – the ELM327 calculates the value and adds

it for you.

[ Warm Start ]

This command causes the ELM327 to perform a

complete reset which is very similar to the AT Z

command, but does not include the power on LED

test. Users may find this a convenient means 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.

[ 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 in the idle state, waiting for

characters on the RS232 bus. Any baud rate set with

the AT BRD command will be reset to the default

setting.

ELM327P Datasheet(PDF) 16 Page - ELM Electronics

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