ELM327P datasheet(10/51 Pages) ELM

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AT Commands (continued)

DM1

[ monitor for DM1s ]

The SAE J1939 Protocol broadcasts trouble codes

periodically as they are detected, using 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 as 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

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

capable

automatically

determining the appropriate OBD protocol to use for

each vehicle that it is connected to. When the IC

connects to a vehicle, however, it returns only the data

requested, and does not report the protocol found. The

DP command is used to determine the current protocol

that

the

ELM327

selected

for

(even

not

connected). If the automatic option is also selected,

the protocol will show the word "AUTO" before it,

followed by the type. Note that the actual protocol

names are displayed, 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 (0) or on(1) ]

These

commands

control

whether

not

characters

received

the

RS232

port

are

retransmitted (or echoed) back to the host computer.

To reduce traffic on the RS232 bus, users may wish to

turn echoing off by issuing ATE0. The default is E1 (or

echo on).

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. More

complete details and examples can be found in the

Altering Flow Control Messages section.

FC SH hhh

[ Flow Control Set Header to… ]

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

used for CAN Flow Control response 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 currently 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 currently only affects Flow Control mode 1.

FC SD [1-5 bytes]

[ Flow Control Set Data to… ]

The data bytes that are sent in a CAN Flow

Control message can be set with this command. The

current version of the software allows one to five data

bytes to be defined, with the remainder of the data

bytes in the message being automatically set to the

default CAN filler byte. Data provided with this

command is only used when Flow Control modes 1 or

2 have been enabled.

H0 and H1

[ Headers off (0) or on(1) ]

These commands control whether or not the

additional (header) bytes of information are shown in

the responses from the vehicle. These are normally

not shown by the ELM327, but can be turned on by

issuing the AT H1 command.

Turning the headers on actually shows more than

just the header bytes – you will see the complete

message as transmitted, including the check-digits and

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