ELM327
OBD to RS232 Interpreter
Description
Almost all of the automobiles produced today
are required, by law, to provide an interface for the
connection of diagnostic test equipment. The data
transfer on these interfaces follow several standards,
but none of them are directly usable by PCs or smart
devices. The ELM327 is designed to act as a bridge
between these On-Board Diagnostics (OBD) ports
and a standard RS232 interface.
In addition to being able to automatically detect
and interpret nine OBD protocols, the ELM327 also
provides support for high speed communications, a
low power sleep mode, and the J1939 truck and bus
standard. It is also completely customizable, should
you wish to alter it to more closely suit your needs.
The following pages discuss all of the ELM327’s
features in detail, how to use it and configure it, as
well as providing some background information on
the protocols that are supported. There are also
schematic diagrams and tips to help you to interface
to microprocessors, construct a basic scan tool, and
to reduce power consumption.
Features
• Power Control with standby mode
• RS232 baud rates to 500 kbps
• Automatically searches for protocols
• Fully configurable with AT commands
• Low power CMOS design
Connection Diagram
PDIP and SOIC
(top view)
MCLR
Vmeasure
J1850 Volts
J1850 Bus+
Memory
Baud Rate
LFmode
V
SS
XT1
XT2
VPW In
ISO In
PWM In
J1850 Bus-
OBD Tx LED
OBD Rx LED
RS232 Tx LED
RS232 Rx LED
CAN Rx
CAN Tx
ISO L
ISO K
V
DD
V
SS
RS232 Rx
RS232 Tx
PwrCtrl / Busy
IgnMon / RTS
Applications
• Diagnostic trouble code readers
• Automotive scan tools
• Teaching aids
Block Diagram
Baud Rate
LFmode
RS232Rx
RS232Tx
6
7
4.00 MHz
Memory
5
XT1
9
10
XT2
MCLR
1
Vmeasure
2
18
17
RS232
Interface
Command
and
Protocol
Interpreter
A/D
Converter
PwrCtrl / Busy
IgnMon / RTS
16
15
Power
Control
ISO 15765-4
SAE J1939
ISO 9141-2
ISO 14230-4
SAE J1850
PWM & VPW
23
25
26
27
28
24
21
22
12
3
4
14
13
11
OBD interfaces
status LEDs
ELM327DSH
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