ELM327
OBD to RS232 Interpreter
Description
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 RS232 ports.
The ELM327 builds on improved versions of our
proven ELM320, ELM322, and ELM323 interfaces
by adding seven CAN protocols to them. The result
is an IC that can automatically sense and convert
the most common protocols in use today. There are
a number of other improvements as well – a high
speed RS232 option, battery voltage monitoring, and
customizable features through programmable
parameters, to name only a few.
The ELM327 requires few external components
to make a fully functioning circuit. The following
pages discuss the interface details, and show how to
use the IC to ‘talk’ to your vehicle, then concludes
with two schematics to get you started.
Features
• Supports 12 protocols
• Automatically searches for a protocol
• Fully configurable with AT commands
• RS232 baud rates to 500Kbps
• Voltage input for battery monitoring
• Low power CMOS design
Connection Diagram
PDIP and SOIC
(top view)
MCLR
Vmeasure
J1850 Volts
J1850 Bus+
Memory
Baud Rate
LFmode
V
SS
XT1
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
Busy
RTS
Applications
• Diagnostic trouble code readers
• Automotive scan tools
• Teaching aids
XT2
VPW In
ISO In
PWM In
J1850 Bus-
4.00 MHz
Block Diagram
Memory
5
XT1
9
10
XT2
MCLR
1
Vmeasure
2
Baud Rate
LFmode
RS232Rx
RS232Tx
RTS
Busy
18
17
6
7
RS232
Interface
Command
and
Protocol
Interpreter
A/D
Converter
CAN
ISO 15765-4
SAE J1939*
ISO 9141-2
ISO 14230-4
SAE J1850
PWM & VPW
15
16
25
…
28
23
24
21
22
12
3
4
14
13
11
status LEDs
OBD interfaces
*some support
ELM327DSC
Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
1 of 51
ELM [ ELM ELECTRONICS ]
