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ELM329
ELM329DSC
Elm Electronics – Circuits for the Hobbyist
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AT Command Descriptions (continued)
while powering up the ELM329 circuit. Hold it in
position until you see the RS232 Receive LED begin to
flash (which indicates that all of the PPs have been
turned off). At this point, remove the jumper to allow
the IC to perform a normal startup. Note that a reset of
the PPs occurs quite quickly – if you are holding the
jumper on for more than a few seconds and do not see
the RS232 receive light flashing, remove the jumper
and try again, as there may be a problem with your
connection.
PP hh ON
[ turn Prog Parameter hh ON ]
This command enables Programmable Parameter
number hh. Once enabled, any value assigned using
the PP hh SV command will be used instead of the
factory default value. (All of the programmable
parameter values are set to their default values at the
factory, so enabling a programmable parameter before
assigning a value to it will not cause problems.) The
actual time when the value for this parameter becomes
effective is determined by its type. Refer to the
Programmable Parameters section (page 64) for more
information on the types.
Note that ‘PP FF ON’ is a special command that
enables all of the Programmable Parameters at the
same time.
PP hh SV yy
[ Prog Parameter hh, Set Value to yy ]
A value is assigned to a Programmable Parameter
using this command. The system will not be able to
use this new value until the Programmable Parameter
has been enabled, with the PP hh ON command.
PPS
[ Programmable Parameter Summary ]
The complete range of Programmable Parameters
are displayed with this command (even those not yet
implemented). Each is shown as a PP number
followed by a colon and the value that is assigned to it.
This is followed by a single digit – either ‘N’ or ‘F’ to
show that it is ON (enabled), or OFF (disabled),
respectively. See the Programmable Parameters
section for a more complete discussion.
R0 and R1
[ Responses off or on ]
These commands control the ELM329’s automatic
receive (and display) of the messages returned by the
vehicle. If responses have been turned off, the IC will
not wait for a reply from the vehicle after sending a
request, and will return immediately to wait for the next
RS232 command (the ELM329 does not print anything
to say that the send was successful, but you will see a
message if it was not).
R0 may be useful to send commands blindly when
using the IC for a non-OBD network application, or
when simulating an ECU in a learning environment. It
is not very useful for normal OBD communications,
however, as the purpose of making request is to obtain
replies.
An R0 setting will always override any ‘number of
responses digit’ that is provided with an OBD request.
The default setting is R1, or responses on.
RD
[ Read the Data in the user memory ]
The byte value stored in the non-volatile user
memory (with the SD command) is retrieved with this
command. There is only one memory location, so no
address is required.
RTR
[ send an RTR message ]
This command causes a special ‘Remote Frame’
CAN message to be sent. This type of message has
no data bytes, and has its Remote Transmission
Request (RTR) bit set. The headers and filters will
remain as previously set (ie the ELM329 does not
make any assumptions as to what format a response
may have), so adjustments may need to be made to
the mask and filter before sending an RTR. This
command must be used with an active CAN protocol
(one that has been sending and receiving messages),
as it can not initiate a protocol search. Note that the
CAF1 setting normally eliminates the display of all
RTRs, so if you are monitoring messages and want to
see the RTRs, you will have to turn off formatting, or
else turn the headers on.
The ELM329 treats an RTR just like any other
message sent, and will wait for a response from the
vehicle (unless AT R0 has been chosen).
RV
[ Read the input Voltage ]
This initiates the reading of the voltage present at
pin 2, and the conversion of it to a decimal voltage. By
default, it is assumed that the input is connected to the
voltage to be measured through a 470K
Ω
and 100K
Ω
resistor divider (with the 100K
Ω
connected from pin 2
to Vss), and that the ELM329 supply is a nominal 5V.
This will allow for the measurement of input voltages