ELM323
OBD (ISO) to RS232 Interpreter
Description
Since the 1996 model year, North American
automobiles have been required to provide an OBD
(On Board Diagnostics) data port for the connection
of test equipment. This port is used to obtain
emissions-related diagnostics information, and in
some cases can also be used to obtain real-time
vehicle operating parameters.
The ELM323 is a 14 pin integrated circuit that,
with only a few external components, is able to
convert between the OBD data format and the
standard RS232 serial data format. This allows
virtually any personal computer or PDA to
communicate with a vehicle using only a standard
serial port and a terminal program. If desired,
hobbyists can even create their own custom ‘scan
tool’ by adding an interface program.
Please note that while this integrated circuit has
undergone significant changes recently, it is still
considered to be an experimenter’s circuit. It does
support a great many of the ISO9141 and ISO14230
(KWP2000) protocol vehicles, but not all of them,
due to the many interpretations of these standards
that are to be found in use.
Features
• Low power CMOS design
• Crystal controlled for accuracy
• ISO 9141-2 and ISO 14230-4 protocols
• Configurable with AT commands
• Standard ASCII character output
• Four high current LED drive outputs
Connection Diagram
PDIP and SOIC
(top view)
V
DD
XT1
XT2
LFmode
RS232Rx
RS232Tx
1
2
3
4
5
6
7
14
13
12
11
10
9
8
V
SS
OBDK
OBDL
OBDIn
OBDTx
OBDRx
RSTx
Applications
• Diagnostic trouble code readers
• Automotive scan tools
• Teaching aids
3.58 MHz
RSRx
Block Diagram
LFmode
4
XT1
2
3
XT2
Timing and
Control
RS232
Interface
Interpreter
OBD
Interface
13
12
OBDK
OBDL
RS232Rx
RS232Tx
5
6
11
OBDIn
RSRx
RSTx
7
8
10
9
OBDTx
OBDRx
ELM323DSD
Elm Electronics – Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
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