ELM327
AT Command Descriptions (continued)
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.
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.
DP
[ Describe the current Protocol ]
FC SH hhhhhhhh
[ Flow Control Set Header to… ]
The ELM327 automatically detects a vehicle’s
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.
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.
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 48).
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 ]
FE
[ Forget Events ]
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).
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),
which blocks subsequent searching through CAN
protocols if PP 2A bit 5 is ‘1’. Normally, an event such
as this will affect all searches until the next power off
and on, but it can be ‘forgotten’ using software, with
the AT FE command.
FC SD [1-5 bytes]
[ Flow Control Set Data to… ]
Another example is an ‘LV RESET’ event which
will prevent searches through CAN protocols if PP 2A
bit 4 is ‘1’. It may also be forgotten with the AT FE
command.
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.
FI
[ perform a Fast Initiation ]
One version of the Keyword protocol uses what is
known as a 'fast initiation' sequence to begin
communications. Usually, this sequence is performed
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