ELM327P datasheet(5/51 Pages) ELM

5 / 51 page

5 of 51

ELM327

ELM327DSC

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

Communicating with the ELM327

The ELM327 expects to communicate with the

host through an RS232 serial connection. Modern

computers

not

usually

provide

physical

connection such as this, but there are several ways in

which a ‘virtual serial port’ can be created. The most

common devices are USB to RS232 adapters, but

there are several others such as ethernet to RS232

devices, or Bluetooth to serial adapters.

No matter how you physically connect to the

ELM327, you will need a way to send and receive

characters. To do this, the simplest method is to use

one of the many ‘terminal’ programs that are available

(HyperTerminal, ZTerm, etc.), to allow typing the

characters directly from your keyboard.

To use a terminal program, you will need to make

several settings. First, ensure that your software is set

to use the proper ‘COM’ port, and that you have

chosen the proper data rate - this will be either 9600

baud (if pin 6=0V at power up), or 38400 baud (if

PP 0C has not been changed). If you select the wrong

“COM” port, you will not be able to send or receive any

data. If you select the wrong data rate, the information

that you send and receive will be all garbled, and

unreadable by you or the ELM327. Don’t forget to also

set your connection for 8 data bits, no parity bits, and 1

stop bit, and to also set it for the proper “line end”

mode. All of the responses from the ELM327 are

terminated with a single carriage return character and,

optionally, a linefeed character (depending on your

settings).

Properly connected and powered, the ELM327 will

energize the four LED outputs in sequence (as a lamp

test) and will then send the message:

ELM327 v1.2

In addition to identifying the version of this IC,

receiving this string is a good way to confirm that the

computer connections and terminal software settings

are correct (however, at this point no communications

have taken place with the vehicle, so the state of that

connection is still unknown). The ‘>’ character that is

shown on the second line is the ELM327’s prompt

character. It indicates that the device is in the idle

state, ready to receive characters on the RS232 port.

Characters sent from the computer can either be

intended for the ELM327’s internal use, or for

reformatting and passing on to the vehicle. The

ELM327 can quickly determine where the received

characters are to be directed by analyzing the entire

string once the complete message has been received.

Commands for the ELM327’s internal use will always

begin with the characters ‘AT’, while OBD commands

for the vehicle are only allowed to contain the ASCII

codes for hexadecimal digits (0 to 9 and A to F).

Whether an ‘AT’ type internal command or a hex

string for the OBD bus, all messages to the ELM327

must be terminated with a carriage return character

(hex ‘0D’) before it will be acted upon. The one

exception is when an incomplete string is sent and no

carriage return appears. In this case, an internal timer

will automatically abort the incomplete message after

about 20 seconds, and the ELM327 will print a single

question mark (‘?’) to show that the input was not

understood (and was not acted upon).

Messages that are not understood by the ELM327

(syntax errors) will always be signalled by a single

question mark. These include incomplete messages,

incorrect AT commands, or invalid hexadecimal digit

strings, but are not an indication of whether or not the

message was understood by the vehicle. One must

keep in mind that the ELM327 is a protocol interpreter

that makes no attempt to assess the OBD messages

for validity – it only ensures that an even number of

hex digits were received, combined into bytes, then

sent out the OBD port, and it does not know if the

Overview

The following describes how to use the ELM327 to

obtain information from your vehicle.

We begin by discussing just how to “talk” to the IC

using a PC, then explain how to change options using

‘AT’ commands, and finally we show how to use the

ELM327 to obtain trouble codes (and reset them). For

the more advanced experimenters, there are also

sections on how to use some of the programmable

features of this product as well.

Using the ELM327 is not as daunting as it first

seems. Many users will never need to issue an ‘AT’

command, adjust timeouts, or change the headers. For

most, all that is required is a PC or a PDA with a

terminal program (such as HyperTerminal or ZTerm),

and knowledge of one or two OBD commands, which

we will provide in the following sections…

ELM327P 数据表(PDF) 5 Page - ELM Electronics

ELM327P 数据表(HTML) 5 Page - ELM Electronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

数据表下载