ELM327P datasheet(15/76 Pages) ELM

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ELM327

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the display of the DLC digit (the headers must also be

on in order to see this digit). When displayed, the

single DLC digit will appear between the ID (header)

bytes and the data bytes. The default setting is

determined by PP 29.

DM1

[ monitor for DM1s ]

The SAE J1939 Protocol broadcasts trouble codes

periodically, by way of Diagnostic Mode 1 (DM1)

messages. This command sets the ELM327 to

continually monitor for this type of message for you,

following

multi-segment

transport

protocols

required. Note that a combination of masks and filters

could be set to provide a similar output, but they would

not allow multiline messages to be detected. The DM1

command adds the extra logic that is needed for

multiline messages.

This command is only available when a CAN

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

formatting. It returns an error if attempted under any

other conditions.

[ Describe the current Protocol ]

The ELM327 automatically detects a vehicle’s

OBD protocol, but does not normally report what it is.

The DP command is a convenient means of asking

what protocol the IC is currently set to (even if it has

not yet ‘connected’ to the vehicle).

If a protocol is chosen and the automatic option is

also selected, AT DP will show the word 'AUTO' before

the protocol description. Note that the description

shows the actual protocol names, not the numbers

used by the protocol setting commands.

DPN

[ Describe the Protocol by Number ]

This command is similar to the DP command, but

it returns a number which represents the current

protocol. If the automatic search function is also

enabled, the number will be preceded with the letter

‘A’. The number is the same one that is used with the

set protocol and test protocol commands.

E0 and E1

[ Echo off or on ]

These commands control whether or not the

characters received on the RS232 port are echoed

(retransmitted) back to the host computer. Character

echo can be used to confirm that the characters sent

to the ELM327 were received correctly. The default is

E1 (or echo on).

FC SD [1-5 bytes]

[ Flow Control Set Data to… ]

The data bytes that are sent in a CAN Flow

Control message may be defined with this command.

One to five data bytes may be specified, with the

remainder of the data bytes in the message being

automatically set to the default CAN filler byte, if

required by the protocol. Data provided with this

command is only used when Flow Control modes 1 or

2 have been enabled.

FC SH hhh

[ Flow Control Set Header to… ]

The header (or more properly ‘CAN ID’) bytes

used for CAN Flow Control messages can be set using

this command. Only the right-most 11 bits of those

provided will be used -

the most significant bit is

always removed. This command only affects Flow

Control mode 1.

FC SH hhhhhhhh

[ Flow Control Set Header to… ]

This command is used to set the header (or ‘CAN

ID’) bits for Flow Control responses with 29 bit CAN ID

systems. Since the 8 nibbles define 32 bits, only the

right-most 29 bits of those provided will be used - the

most significant three bits are always removed. This

command only affects Flow Control mode 1.

FC SM h

[ Flow Control Set Mode to h ]

This command sets how the ELM327 responds to

First Frame messages when automatic Flow Control

responses are enabled. The single digit provided can

either be ‘0’ (the default) for fully automatic responses,

‘1’ for completely user defined responses, or ‘2’ for

user defined data bytes in the response. Note that FC

modes 1 and 2 can only be enabled if you have

defined the needed data and possibly ID bytes. If you

have not, you will get an error. More complete details

and examples can be found in the Altering Flow

Control Messages section (page 46).

[ Forget Events ]

There are certain events which may change how

the ELM327 responds from that time onwards. One of

these is the occurrence of a fatal CAN error (ERR94),

AT Command Descriptions (continued)

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