ELM322
AT Commands
Several parameters within the ELM322 can be
‘OK’ on the successful completion of a command, so
the user knows that it has been executed.
adjusted in order to modify its behaviour. These do not
normally have to be changed before attempting to talk
to the vehicle, but occasionally the user may wish to
customize the settings, for example by turning the
character echo off, adjusting the timeout value, or
changing the header addresses. In order to do this,
internal ‘AT’ commands must be issued.
Those familiar with PC modems will immediately
recognize AT commands as a standard way in which
modems are internally configured. The ELM322 uses
essentially the same method, always watching the
data sent by the PC, looking for messages that begin
with the character ‘A’ followed by the character ‘T’. If
found, the next characters will be interpreted as
internal configuration or ‘AT’ commands, and will be
executed upon receipt of a terminating carriage return
character. The ELM322 will reply with the characters
Some of the following commands allow the
passing of numbers as arguments in order to set the
internal values. These numbers will always be in
hexadecimal format, and must be provided in pairs.
The hexadecimal conversion chart in the next section
may prove useful if you wish to interpret the values.
Also, one should be aware that for the on/off types of
commands, the second character will be either the
number 1 or 0, the universal terms for on and off.
The following is a summary of all of the AT
commands that are recognized by the current version
of the ELM322, sorted alphabetically. Users of
previous versions of this product (v1.x) should note
that their ICs will only support the E, H and Z options.
AR
[ Automatically set the Receive address ]
E0 and E1
[ Echo off (0) or on (1) ]
Responses from the vehicle will be acknowledged
and displayed by the ELM322, if its internally stored
receive address matches the address that the
message is being sent to. With the Auto Receive
mode in effect, the value used for the receive
address will be chosen based on the current header
bytes, and will automatically be updated whenever
the header bytes are changed.
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).
FD
[ send Formatted Data ]
This command requests that all responses be
returned as standard ASCII characters, which are
readable with virtually any terminal program. Hex
digits are shown as two ASCII characters, and
spaces are provided between each byte as a
separator. Also, every line will end with a carriage
The value that is used for the receive address is
determined based on the contents of the first header
byte. If it shows that the message uses physical
addressing, the third byte of the header is used for
the receive address, otherwise (for functional
addressing) the second header byte, increased in
value by 1, will be used. Auto Receive is turned on
by default.
return character and (optionally)
a
linefeed
character, ensuring that every response appears on
a new line. This is the default mode.
D
[ set all to Defaults ]
H0 and H1
[ Headers off (0) or on (1) ]
This command is used to set the E, H, L, and R
options to their default (or factory) settings, as when
power is first applied. Additionally, the Auto Receive
mode (AR) will be selected, data will be transmitted
in the standard formatted way (as if chosen by FD),
the ‘NO DATA’ timeout will be set to its default value,
and the header bytes will be set to the proper values
for OBDII (SAE J1979) operation.
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 ELM322. To see this extra
information, users can turn the headers on by
issuing an ATH1. The default is H0 (headers off).
ELM322DSF
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