ELM327P datasheet(22/76 Pages) ELM

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ELM327

ELM327DSH

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AT Command Descriptions (continued)

RS232 command (the ELM327 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 recommended that this option used for normal

OBD communications, however, as the vehicle may

have difficulty if it is expecting an acknowledgement

and never receives one.

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.

RA hh

[ set the Receive Address to hh ]

Depending on the application, users may wish to

manually set the address to which the ELM327 will

respond. Issuing this command will turn off the AR

mode, and force the IC to only accept responses

addressed to hh. Use caution with this setting, as

depending on what you set it to, you may end up

accepting (ie. acknowledging with an IFR) a message

that was actually meant for another module. To turn off

the RA filtering, simply send AT AR.

This command is not very effective for use with the

CAN protocols, as it only monitors for one portion of

the ID bits, and that is not likely enough for most CAN

applications - the CRA command may be a better

choice. Also, this command has no effect on the

addresses used by the J1939 protocols, as the J1939

routines derive them from the header values, as

required by the SAE standard.

The RA command is exactly the same as the SR

command, and can be used interchangeably. Note that

CAN Extended Addressing does not use this value - it

uses the one set by the AT TA command.

[ Read the Data in the user memory ]

The byte value stored 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 ELM327 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. 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 ELM327 treats an RTR just like any other

message sent, and will wait for a response from the

vehicle (unless AT R0 has been chosen).

[ 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 47K

Ω and 10KΩ

resistor divider (with the 10K

Ω connected from pin 2 to

Vss), and that the ELM327 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%.

S0 and S1

[ printing of Spaces off or on ]

These commands control whether or not space

characters are inserted in the ECU response.

The ELM327 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. By

default, spaces are on (S1), and space characters are

inserted in every response.

SD hh

[ Save Data byte hh ]

The ELM327 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.

ELM327P Datasheet(PDF) 22 Page - ELM Electronics

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