ELM323
AT Commands (continued)
E0 and E1
[ Echo off (0) or on(1) ]
L0 and L1
[ Linefeeds off (0) or on(1) ]
These commands control whether or not
characters received on 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
(echo on).
Whether or not the ELM323 transmits a linefeed
character after each carriage return character is
controlled by this option. If an ATL1 is issued, linefeed
generation will be turned on, and for AT L0, it will be
off. Users may wish to have this option on if using a
terminal program, but off if using a custom interface
(as the extra characters transmitted will only serve to
slow the vehicle polling down). The default setting is
determined by the level at pin 4 when the IC is reset
(power-on or AT Z), or when the default values are
restored (AT D).
FD
[ send Formatted Data ]
This command requests that all of the vehicle’s
responses be returned as standard ASCII characters
(which are readable with virtually all terminal
programs). Byte values are sent as a pair of ASCII
characters, each representing a hexadecimal digit,
with a space character sent between each pair as a
separator. Every line will end with a carriage return
MA
[ Monitor All messages ]
Using this command places the ELM323 into a
bus monitoring mode, in which it displays all messages
as it sees them on the OBD bus. This continues
indefinitely until stopped by activity on the RS232
input. To stop the monitoring, one should send any
single character then wait for the ELM323 to respond
with a prompt character (‘>’). Waiting for the prompt is
necessary as the response time is unpredictable,
varying depending on what the IC was doing when
interrupted. If, for instance, it was in the middle of
printing a line, it will first complete the line then return
to the command state, then issue the prompt
character. If the ELM323 was simply waiting for OBD
input, it would return immediately. The character which
stops the monitoring will always be discarded, and will
not affect subsequent commands.
character and (optionally)
a
linefeed character,
ensuring that each response appears on a new line.
This is the default output mode.
FI
[ perform a Fast bus Init ]
Issuing this command forces the ELM323 to
perform a fast (KWP / ISO14230) bus initialization
sequence, regardless of the present state of the bus.
Note that the bus does not need to be manually
initalized with this command, as it will be performed
automatically by the ELM323 when required. (It will
first try a slow initialization, and if it is not successful, it
will then attempt a fast initialization sequence.)
This command has been provided as
a
convenience, and should be used with caution. No
periodic ‘wakeup’ messages are sent by the ELM323
while monitoring the bus in this mode, so if the bus
had been initialized before this command was invoked,
the vehicle connection will likely ‘go to sleep’ and will
have to be re-initialized. The ELM323 will not be aware
that the connection was lost, however, and will likely
have to be reset with an AT SW 00, or an AT Z
command.
H0 and H1
[ Headers off (0) or on(1) ]
These commands control whether or not the
header information is shown in the responses. All OBD
messages have an initial (header) string of three bytes
and a trailing check digit, which are normally not
displayed by the ELM323. To see this extra
information, users can turn the headers on by issuing
an ATH1. The default is H0 (headers off).
I
[ Identify yourself ]
PD
[ send Packed Data ]
Issuing this command causes the chip to identify
This option is for those that are building a
itself, by printing the startup product ID string (this is
currently ‘ELM323 v2.0’). Software can use this to
determine exactly which version of the integrated
circuit it is connected to, without having to reset the IC.
computer interface and want the fastest data transfer
rate possible while still operating at 9600 baud. When
selected, all of the data obtained from the vehicle will
be sent as a single length byte, followed by the actual
ELM323DSD
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