ELM329
AT Commands
Several parameters within the ELM329 can be
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 these settings – for example by turning the
character echo off, adjusting a timeout value, or
changing the header (ID) bytes. In order to do this,
internal ‘AT’ commands must be used.
Those familiar with PC modems will immediately
recognize AT commands as a standard way in which
modems are internally configured. The ELM329 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 an
internal configuration or ‘AT’ command, and will be
executed upon receipt of a terminating carriage return
character. If the command is just a setting change, the
ELM329 will reply with the characters ‘OK’, to say that
it was successfully completed.
Some of the commands require that numbers be
provided as arguments, in order to set the internal
values. These will always be hexadecimal numbers
which must generally be provided in pairs. The
hexadecimal conversion chart in the OBD Commands
section (page 26) may be helpful if you wish to
interpret the values. Also, one should be aware that for
the on/off types of commands, the second character is
the number 1 or the number 0, the universal terms for
on and off.
The remainder of this page, and the next page
following provide a summary of all of the commands
that the current version of the ELM329 recognizes. A
more complete description of each command begins
AT Command Summary
ELM329 Options
<CR>
repeat the last command
BRD hh
try Baud Rate Divisor hh
BRT hh
set Baud Rate Timeout
D
set all to Defaults
E0, E1
Echo off, or on*
I
print the version ID
L0, L1
Linefeeds off, or on
LP
go to low power mode
M0, M1
Memory off, or on
RD
Read the stored Data
SD hh
Save Data byte hh
WS
Warm Start (quick software reset)
Z
reset all
@1
display the device description
@2
display the device identifier
@3 cccccccccccc
store the @2 identifier
Programmable Parameters
PP xx OFF
PP FF OFF
PP xx ON
PP FF ON
PP xx SV yy
PPS
Voltage Readings
CV dddd
CV 0000
RV
Other
C0, C1
IGN
IN1
IN2
Control Output off*, or on
read the IgnMon input level
read INput 1 level
read INput 2 level
Calibrate the Voltage to dd.dd volts
restore CV value to factory setting
Read the input Voltage
disable Prog Parameter xx
all Prog Parameters disabled
enable Prog Parameter xx
all Prog Parameters enabled
for PP xx, Set the Value to yy
print a PP Summary
Note:
Settings shown with an asterisk (*)
are the default values
Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
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ELM329DSB
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