ELM329
AT Command Descriptions (continued)
PP hh SV yy [ Prog Parameter hh, Set Value to yy ]
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.
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.
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 470KW and 100KW
resistor divider (with the 100KW connected from pin 2
to Vss), and that the ELM329 supply is a nominal 5V.
This will allow for the measurement of input voltages
up to about 28V, with an uncalibrated accuracy of
typically about 2%.
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).
S0 and S1
[ printing of Spaces off or on ]
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.
These commands control whether or not space
characters are inserted in the ECU response.
The ELM329 normally reports ECU responses as
a series of hex characters that are separated by space
characters (to improve readability), but messages can
be transferred much more quickly if every third byte
(the space) is removed. While this makes the message
less readable for humans, it can provide significant
improvements for computer processing of the data,
and reduce the amount of data in the send buffer. By
default, spaces are on (S1), and space characters are
inserted in every response.
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.
SD hh
[ Save Data byte hh ]
The ELM329 is able to save one byte of
information for you in a special nonvolatile memory
location, which is able to retain its contents even if the
power is turned off. Simply provide the byte to be
stored, then retrieve it later with the read data (AT RD)
command. This location is ideal for storing user
preferences, unit ids, occurrence counts, or other
information.
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
ELM329DSB
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