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ELM322 데이터시트 PDF




ELM Electronics에서 제조한 전자 부품 ELM322은 전자 산업 및 응용 분야에서
광범위하게 사용되는 반도체 소자입니다.


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부품번호 ELM322 기능
기능 OBD (VPW) to RS232 Interpreter
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ELM322 데이터시트, 핀배열, 회로
ELM322
OBD (VPW) to RS232 Interpreter
Description
Since the 1996 model year, North American
automobiles have been required to provide an OBD,
or On Board Diagnostics, port for the connection of
test equipment. Data is transferred serially between
the vehicle and the external equipment using this
connection, in a manner specified by the Society of
Automotive Engineers (SAE) standards. In addition
to operating at different voltage levels, these ports
also use a data format that is not compatible with the
standard used for personal computers.
The ELM322 is an 8 pin integrated circuit that is
www.DataSheeatb4leU.tcoocmhange the data rate and reformat the OBD
signals into easily recognized ASCII characters. This
allows virtually any personal computer to
communicate with an OBD equipped vehicle using
only a standard serial port and a terminal program.
By also enhancing it with an interface program,
hobbyists can create their own custom scan tool.
This integrated circuit was designed to provide a
cost-effective way for experimenters to work with an
OBD system, so a few features such as RS232
handshaking, variable baud rates, etc., have not
been implemented. In addition, this device is only
able to communicate using the 10.4KHz J1850 VPW
protocol that is commonly used in General Motors
and some Daimler Chrysler vehicles.
Applications
• Diagnostic trouble code readers
• Automotive scan tools
Features
• Low power CMOS design
• High current drive outputs - up to 25 mA
• Crystal controlled for accuracy
• Fully configurable using AT commands
• Standard ASCII character output
• High speed RS232 communications
• 10.4 KHz J1850 VPW protocol
Connection Diagram
PDIP and SOIC
(top view)
VDD 1
XT1 2
XT2 3
OBDIn 4
8 VSS
7 OBDOut
6 Tx
5 Rx
Block Diagram
3.58 MHz
XT1 2
3 XT2
Timing and
Control
Tx 6
Rx 5
RS232
Interface
Interpreter
OBD
Interface
4 OBDIn
7 OBDOut
ELM322DSE
Elm Electronics – Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
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ELM322 pdf, 반도체, 판매, 대치품
ELM322
Overview
The following describes how to use the ELM322 to
obtain a great deal of information from your vehicle. To
some, the quantity of information will be overwhelming,
and for others it will not be enough.
We begin by discussing just how to talk to the IC,
then how to adjust some options through the use of
‘AT’ commands, and finally go on to actually talk to the
vehicle, obtaining trouble codes and resetting them.
For the more advanced experimenters, there are also
sections on how to use some of the programmable
features of this product as well.
It is not as daunting as it first appears. 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 provide in the
following…
Communicating with the ELM322
www.DataSheet4UTh.ceomELM322 relies on a standard RS232 type
serial connection to communicate with the user. The
data rate is fixed at 9600 baud, with 8 data bits, no
parity bit, 1 stop bit, and no handshaking (often
referred to as 9600 8N1). All responses from the IC
are terminated with a single carriage return character
and, by default, a line feed character as well. Make
sure your software is configured properly for the mode
you have chosen.
Properly connected and powered, the ELM322 will
initially display the message:
ELM322 v2.0
>
In addition to identifying the version of the IC,
receipt of this string is a convenient way to be sure
that the computer connections and the settings are
correct. However, at this point no communications
have taken place with the vehicle, so the state of the
OBD connection is still unknown.
The ‘>’ character displayed above is the ELM322’s
prompt character. It indicates that the device is in its
idle state, ready to receive characters on the RS232
port. Characters sent from the computer can either be
intended for the ELM322’s internal use, or for
reformatting and passing on to the vehicle’s OBD bus.
Commands for the ELM322 are distinguished from
those to the vehicle by always beginning with the
characters ‘AT’ (as is common with modems), while
commands for the OBD bus can contain only the
ASCII characters for hexadecimal digits (0 to 9 and A
to F). This allows the ELM322 to quickly determine
where the received characters are to be directed.
Whether an ‘AT’ type internal command or a hex
string for the OBD bus, all messages to the ELM322
must be terminated with a carriage return character
(hex ‘0D’) before they will be acted upon. If an
incomplete string is sent and no carriage return
appears, an internal timer will automatically abort the
incomplete message after about 10 seconds. Should
this happen, the ELM322 will print a single question
mark to show that the input was not understood (and
was ignored).
Messages that are misunderstood by the ELM322
(syntax errors) will always be signalled by a single
question mark (‘?’). These include incomplete
messages, invalid hexadecimal digit strings, or
incorrect AT commands. It is not an indication of
whether or not the message was understood by the
vehicle. (The ELM322 is a protocol interpreter that
makes no attempt to assess OBD messages for
validity – it only ensures that an even number of hex
digits were received, combined into bytes, and sent
out the OBD port, so it cannot determine if the
message sent to the vehicle is in error.)
Incomplete or misunderstood messages can also
occur if the controlling computer attempts to write to
the ELM322 before it is ready to accept the next
command (as there are no handshaking signals to
control the data flow). To avoid a data overrun, users
should always wait for the prompt character (‘>’)
before issuing the next command.
Finally, a few convenience items to note. The
ELM322 is not case-sensitive, so ‘ATZ’ is equivalent to
‘atz’, and to ‘AtZ’. The device ignores space characters
as well as control characters (tab, linefeed, etc.) in the
input, so they can be inserted anywhere to improve
readability, and finally, issuing only a single carriage
return character will repeat the last command (making
it easier to request updates on dynamic data such as
engine rpm).
ELM322DSE
Elm Electronics – Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
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ELM322 전자부품, 판매, 대치품
AT Commands (continued)
SR hh
[ Set the Receive address to hh ]
Depending on the application, users may wish to
manually set the address to which the ELM322 will
respond. Issuing this command will turn off the AR
mode, and force the IC to only accept responses
addressed to hh. This could be useful in non-OBD
applications, or simply while experimenting with a
network.
ST hh
[ Set Timeout to hh ]
After sending a request, the ELM322 waits a preset
time before declaring that there was no response
www.DataSheefDtr4oeUmp.ecnodtmhineg
vehicle
on the
(the ‘NO
application
DATA’ response).
(and priority of the
request), users may want to modify this timeout
period before the ELM322 declares that the request
was a failure. The ST command is used to do that.
The actual time used is (approximately) 4 ms x the
byte value passed as the hexadecimal argument.
Passing a value of FF thus results in a maximum
time of about 1020 ms. Values less than 08 will be
ignored and forced to a value of 8, providing a
minimum time of 32 ms. The default value is 32
(decimal 50) providing a timeout of 200 ms.
Z [ reset all ]
This command causes the chip to perform a
complete reset, as if power were cycled off and then
on again. All settings are returned to their default
values, and the chip will be put in the idle state,
waiting for characters on the RS232 bus.
AT Command Summary
Figure 1 (at the right) shows all of the ELM322
commands in one convenient chart. In order to help
with the understanding of these, we have grouped
the commands into three functional areas, but this
has no bearing on how the commands should be
used, it is only for clarity. You may find this chart to
be useful when experimenting with the IC.
ELM322
ELM322 AT Commands
general
D set all to Defaults
I show the ID string
Z reset all
<CR> repeat last command
responses
E1/0 Echo on/off
H1/0 Headers on/off
L1/0 Linefeeds on/off
R1/0 Responses on/off
PD use Packed Data
FD use Formatted Data
ST hh Set Timeout (hh*4ms)
requests
SH xx yy zz Set Header
SR hh Set Rx address
AR Auto Receive
MA Monitor All
MR hh Monitor for Rxer hh
MT hh Monitor for Txer hh
Figure 1. ELM322 AT Commands
ELM322DSE
Elm Electronics – Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
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