ELM327P datasheet(13/51 Pages) ELM

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ELM327

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AT Commands (continued)

are always assumed to be 00. For example, the DM2

PGN has an assigned

value of 00FECB (see SAE

J1939-73). To monitor for all DM2 messages, you

would issue AT MP FECB, eliminating the 00, since

the ELM327 always assumes that the PGN is

preceeded by these two zeros.

This command is only available when a CAN

Protocol (A, B, or C) has been selected for SAE J1939

formatting. It returns an error if attempted under any

other conditions. Note also that this version of the

ELM327 only displays responses that match the

criteria, not the requests that are asking for the

information.

MR hh

[ Monitor for Receiver hh ]

This command also places the IC in a bus

monitoring mode, displaying only messages that were

sent to the hex address given by hh. These are

messages which are found to have the value hh in the

second byte of a traditional three byte OBD header, in

bits 8 to 15 of a 29 bit CAN ID, or in bits 8 to 10 of an

11 bit CAN ID. Any single RS232 character aborts the

monitoring, as with the MA command.

MT hh

[ Monitor for Transmitter hh ]

This command places the IC in a bus monitoring

mode, displaying only messages that were sent by the

transmitter at the hex address given by hh. These are

messages which are found to have that value in the

third byte of a traditional three byte OBD header, or in

bits 0 to 7 for CAN IDs. As with the MA and MR

monitoring

modes,

any

RS232

activity

(single

character) aborts the monitoring.

[ Normal Length messages ]

Setting the NL mode on forces all sends and

receives to be limited to the standard seven data bytes

in length, similar to the other ELM32x OBD ICs. To

allow longer messages, use the AL command.

Beginning with v1.2, the ELM327 does not require

a change to AL to allow longer message lengths for

the KWP protocols to be received (as determined by

the header length values). You can simply leave the IC

set to the default setting of NL, and all of the received

bytes will be shown.

[ Protocol Close ]

There may be occasions where it is desirable to

stop (deactivate) a protocol. Perhaps you are not using

the automatic protocol finding, and wish to manually

activate and deactivate protocols. Perhaps you wish to

stop the sending of idle (wakeup) messages, or have

another reason. The PC command is used in these

cases to force a protocol to close.

PP hh OFF

[ turn Prog. Parameter hh OFF ]

This command disables Programmable Parameter

number hh. Any value assigned using the PP hh SV

command will no longer be used, and the factory

default setting will once again be in effect. The actual

time when the new value for this parameter becomes

effective is determined by its type. Refer to the

Programmable

Parameters

section

for

information on the types.

Note that ‘PP FF OFF’ is a special command that

disables all of the Programmable Parameters, as if you

had entered PP OFF for every possible one.

It is possible to alter some of the Programmable

Parameters so that it may be difficult, or even

impossible, to communicate with the ELM327. If this

occurs, there is a hardware means of resetting all of

the Programmable Parameters at once. Connect a

jumper from circuit common to pin 28, holding it there

while powering up the ELM327 circuit. Hold it in

position until you see the RS232 Receive LED begin to

flash (which indicates that all of the PPs have been

turned off). At this point, remove the jumper to allow

the IC to perform a normal startup. Note that a reset of

the PPs occurs quite quickly – if you are holding the

jumper on for more than a few seconds and do not see

the RS232 receive light flashing, remove the jumper

and try again – there may be a problem with your

connection. This feature is only available beginning

with v1.2, and is not a provided with any earlier

versions of the ELM327 IC.

PP hh ON

[ turn Programmable Parameter hh ON ]

This command enables Programmable Parameter

number hh. Once enabled, any value assigned using

the PP hh SV command will be used where the factory

default value was before. Note that all programmable

parameter values are set to ‘FF’ at the factory, so

enabling a programmable parameter before assigning

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