ELM327
Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
OBD to RS232 Interpreter
Almost all new automobiles produced today are
required, by law, to provide an interface from which
test equipment can obtain diagnostic information.
The data transfer on these interfaces follow several
standards, none of which are directly compatible
with PCs or PDAs. The ELM327 is designed to act
as a bridge between these On-Board Diagnostics
(OBD) ports and standard PC RS232 ports.
The ELM327 builds on improved versions of our
proven ELM320, ELM322, and ELM323 interfaces
by adding four CAN protocols to them. The result is
an IC that can automatically sense and convert the
nine most common protocols in use today. There are
a number of other improvements as well - a high
speed RS232 option with data buffering, battery
voltage monitoring, and the ability to remember the
last used protocol, to name only a few.
The following is only a “Quick Summary” of the
ELM327. For Example Applications, and a more
detailed discussion of the many features, download
the full datasheet.
• Supports 9 OBDII protocols
• Automatically searches for a protocol
• Fully configurable with AT commands
• High and Medium speed RS232
• Voltage input for battery monitoring
• Low power CMOS design
• Diagnostic trouble code readers
• Automotive scan tools
• Teaching aids
Description
Applications
Block Diagram
Features
ELM327QSA
Connection Diagram
PDIP and SOIC
(top view)
OBD Tx LED
OBD Rx LED
RS232 Tx LED
RS232 Rx LED
CAN Rx
CAN Tx
ISO L
ISO K
VDD
RS232 Rx
RS232 Tx
Busy
RTS
MCLR
Memory
Baud Rate
LFmode
J1850 Volts
XT1
XT2
VSS
ISO In
PWM In
J1850 Bus+
VPW In
J1850 Bus-
Vmeasure
VSS
1 of 5
9
10
XT1
XT2
18
17
Command
and
Protocol
Interpreter
6
RS232Tx
RS232Rx
LFmode
4.00 MHz
RS232
Interface
2
7
12
24
23
22
21
ISO 15765-4
CAN
ISO 9141-2
ISO 14230-4
SAE J1850
PWM & VPW
11
13
4
3
14
A/D
Converter
15
16
Baud Rate
25
28
…
5
Memory
status LEDs
OBD interfaces
1
Busy
MCLR
Vmeasure
RTS
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