2024年4月9日发(作者：承紫南)
元器件交易网
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-
Block Diagram
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ELM327
Pin Descriptions
MCLR (pin 1)
A momentary logic low applied to this input will reset
the IC. If unused, this pin should be connected to a
logic high (V
DD
) level.
Vmeasure (pin 2)
This analog input is used to measure a 0 to 5V
signal that is applied to it. Care must be taken to
prevent the voltage from going outside of the supply
levels of the ELM327, or damage may occur. If it is
not used, this pin should be tied to either V
DD
or V
SS
.
J1850 Volts (pin 3)
This output can be used to control a voltage supply
for the J1850 Bus+ output. The pin will output a logic
high level when a nominal 8V is required (for J1850
VPW), and will output a low level when 5V is needed
(as for J1850 PWM applications). If this switching
capability is not required for your application, this
output can be left open-circuited.
J1850 Bus+ (pin 4)
This active high output is used to drive the
J1850 Bus+ Line to an active level. Note that this
signal does not have to be used for the Bus- Line (as
was the case for the ELM320), since a separate
J1850 Bus- drive output is provided on pin 14.
Memory (pin 5)
This input controls the default state of the memory
option. If this pin is at a high level during power-up or
reset, the memory function will be enabled by
default. If it is at a low level, then the default will be
to have it disabled. Memory can always be enabled
or disabled with the AT M1 and AT M0 commands.
Baud Rate (pin 6)
This input controls the baud rate of the RS232
interface. If it is at a high level during power-up or
reset, the baud rate will be set to 38400 (or the
rate that has been set by PP 0C). If at a low level,
the baud rate will be 9600.
LFmode (pin 7)
This input is used to select the default linefeed
mode to be used after a power-up or system reset.
If it is at a high level, then by default messages
sent by the ELM327 will be terminated with both a
carriage return and a linefeed character. If it is at a
low level, lines will be terminated by a carriage
return only. This behaviour can always be modified
by issuing an AT L1 or AT L0 command (see the
section on AT Commands).
V
SS
(pins 8 and 19)
Circuit common must be connected to these pins.
XT1 (pin 9) and XT2 (pin 10)
A 4.000 MHz oscillator crystal is connected
between these two pins. Loading capacitors as
required by the crystal (typically 27pF each) will
also need to be connected between each of these
pins and circuit common (Vss).
Note that this device has not been configured for
operation with an external oscillator – it expects a
crystal to be connected to these pins. Use of an
external clock source is not recommended.
VPW In (pin 11)
This is the active high input for the J1850 VPW
data signal. When at rest (bus recessive) this pin
should be at a low logic level. This input has
Schmitt trigger waveshaping, so no special
amplification is required.
All rights reserved. Copyright 2005, 2006, and 2007 by Elm Electronics Inc.
Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be
given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information
described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these
products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or
systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve
reliability, function, or design.
ELM327DSC
Elm Electronics – Circuits for the Hobbyist
2 of 51
2024年4月9日发(作者：承紫南)
元器件交易网
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-
Block Diagram
ELM327DSC
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1 of 51
元器件交易网
ELM327
Pin Descriptions
MCLR (pin 1)
A momentary logic low applied to this input will reset
the IC. If unused, this pin should be connected to a
logic high (V
DD
) level.
Vmeasure (pin 2)
This analog input is used to measure a 0 to 5V
signal that is applied to it. Care must be taken to
prevent the voltage from going outside of the supply
levels of the ELM327, or damage may occur. If it is
not used, this pin should be tied to either V
DD
or V
SS
.
J1850 Volts (pin 3)
This output can be used to control a voltage supply
for the J1850 Bus+ output. The pin will output a logic
high level when a nominal 8V is required (for J1850
VPW), and will output a low level when 5V is needed
(as for J1850 PWM applications). If this switching
capability is not required for your application, this
output can be left open-circuited.
J1850 Bus+ (pin 4)
This active high output is used to drive the
J1850 Bus+ Line to an active level. Note that this
signal does not have to be used for the Bus- Line (as
was the case for the ELM320), since a separate
J1850 Bus- drive output is provided on pin 14.
Memory (pin 5)
This input controls the default state of the memory
option. If this pin is at a high level during power-up or
reset, the memory function will be enabled by
default. If it is at a low level, then the default will be
to have it disabled. Memory can always be enabled
or disabled with the AT M1 and AT M0 commands.
Baud Rate (pin 6)
This input controls the baud rate of the RS232
interface. If it is at a high level during power-up or
reset, the baud rate will be set to 38400 (or the
rate that has been set by PP 0C). If at a low level,
the baud rate will be 9600.
LFmode (pin 7)
This input is used to select the default linefeed
mode to be used after a power-up or system reset.
If it is at a high level, then by default messages
sent by the ELM327 will be terminated with both a
carriage return and a linefeed character. If it is at a
low level, lines will be terminated by a carriage
return only. This behaviour can always be modified
by issuing an AT L1 or AT L0 command (see the
section on AT Commands).
V
SS
(pins 8 and 19)
Circuit common must be connected to these pins.
XT1 (pin 9) and XT2 (pin 10)
A 4.000 MHz oscillator crystal is connected
between these two pins. Loading capacitors as
required by the crystal (typically 27pF each) will
also need to be connected between each of these
pins and circuit common (Vss).
Note that this device has not been configured for
operation with an external oscillator – it expects a
crystal to be connected to these pins. Use of an
external clock source is not recommended.
VPW In (pin 11)
This is the active high input for the J1850 VPW
data signal. When at rest (bus recessive) this pin
should be at a low logic level. This input has
Schmitt trigger waveshaping, so no special
amplification is required.
All rights reserved. Copyright 2005, 2006, and 2007 by Elm Electronics Inc.
Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be
given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information
described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these
products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or
systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve
reliability, function, or design.
ELM327DSC
Elm Electronics – Circuits for the Hobbyist
2 of 51