ELM327P datasheet(20/76 Pages) ELM

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ELM327

ELM327DSH

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AT Command Descriptions (continued)

This allows for future expansion, should additional

PGNs be defined with the Data Page bit set. Note that

only the Data Page bit is relevant in the extra byte -

the other bits are ignored.

MP hhhhhh n

[ Monitor for PGN, get n messages ]

This is very similar to the previous command, but it

adds the ability to set the number of messages that

should be fetched before the ELM327 automatically

stops monitoring and prints a prompt character. The

value ‘n’ may be any single hex digit.

MR hh

[ Monitor for Receiver hh ]

This command is very similar to the AT MA

command except that it will only display 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.

Note that if this command is used with CAN

protocols, and if the CAN filter and/or mask were

previously set (with CF, CM or CRA), then the MR

command will over-write the previous values for these

bits only - the others will remain unchanged. As an

example, if the receive address has been set with

CRA 4B0, and then you send MR 02, the 02 will

replace the 4, and the CAN masks/filters will only allow

IDs that are equal to 2B0. This is often not what is

desired - you may want to reset the masks and filters

(with AT AR) first.

As with the AT MA command, this command

begins by performing an internal Protocol Close.

Subsequent OBD requests may show ‘SEARCHING’

or ‘BUS INIT’, etc. messages when the protocol is

reactivated.

MT hh

[ Monitor for Transmitter hh ]

This command is also very similar to the AT MA

command, except that it will only display messages

that were sent by the transmitter with 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.

Note that if this command is used with CAN

protocols, and if the CAN filter and/or mask were

previously set (with CF, CM or CRA), then the MT

command will over-write the previous values for these

bits only - the others will remain unchanged. As an

example, if the receive address has been set with

CRA 4B0, and then you send MT 20, the 20 will

replace the B0, and the CAN masks/filters will only

allow IDs that are equal to 420. This is often not what

is desired - you may want to reset the masks and

filters (with AT AR) first.

As with the AT MA command, this command

begins by performing an internal Protocol Close.

Subsequent OBD requests may show ‘SEARCHING’

or ‘BUS INIT’, etc. messages when the protocol is

reactivated.

[ 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.

PB xx yy

[ set Protocol B parameters ]

This command allows you to change the protocol

B (USER1) options and baud rate without having to

change the associated Programmable Parameters.

This allows for easier testing, and program control.

To use this feature, simply set xx to the value for

PP 2C, and yy to the value for PP 2D, and issue the

command. The next time that the protocol is initialized

it will use these values. For example, assume that you

wish to try monitoring a system that uses 11 bit CAN at

33.3 kbps. If you do not want any special formatting,

this means a value of 11000000 or C0 for PP 2C, and

15 decimal or 0F hex for PP 2D. Send these values to

the ELM327 in one command:

>AT PB C0 0F

then monitor:

>AT MA

if you see CAN ERRORs, and realize that you wanted

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