ELM327 Datasheet PDF - ELM
| Part Number | ELM327 | |
| Description | OBD to RS232 Interpreter | |
| Manufacturers | ELM | |
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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 serial 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 use the low power mode.
Applications
• Diagnostic trouble code readers
• Automotive scan tools
• Teaching aids
Features
• Power Control with standby mode
• Universal serial (RS232) interface
• 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
VSS
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
VDD
VSS
RS232 Rx
RS232 Tx
PwrCtrl / Busy
IgnMon / RTS
Block Diagram
4.00 MHz
Baud Rate 6
LFmode 7
Memory
5
RS232Rx 18
RS232Tx 17
RS232
Interface
PwrCtrl / Busy 16
IgnMon / RTS 15
Power
Control
XT1 9
10 XT2
Command
and
Protocol
Interpreter
25 26 27 28
status LEDs
MCLR
1
A/D
Converter
Vmeasure
2
ISO 15765-4
SAE J1939
ISO 9141-2
ISO 14230-4
SAE J1850
PWM & VPW
23 24
21 22 12
OBD interfaces
3 4 14 13 11
ELM327DSJ
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ELM327
Pin Descriptions (continued)
IgnMon / RTS (pin 15)
This input pin can serve one of two functions,
depending on how the Power Control options
(PP 0E) are set.
If both bit 7 and bit 2 of PP 0E are ‘1’s, this pin will
act as an Ignition Monitor. This will result in a switch
to the Low Power mode of operation, should the
IgnMon signal go to a low level, as would happen if
the vehicle’s ignition were turned off. An internal
‘debounce’ timer is used to ensure that the ELM327
does not shut down for noise at the input.
When the voltage at pin 15 is again restored to a
high level, and a time of 1 or 5 seconds (as set by
PP 0E bit 1) passes, the ELM327 will perform a
‘Warm Start’ and return to normal operation. A low to
high transition at pin 15 will in fact restore normal
operation, regardless of the setting of PP 0E bit 2, or
whether pin 15 was the initial cause for the low
power mode. This feature allows a system to control
how and when it switches to low power standby
operation, but still have automatic wakeup by the
ignition voltage, or even by a pushbutton.
If either bit 7 or bit 2 of PP 0E are ‘0’, this pin will
function as an active low ‘Request To Send’ input.
This can be used to interrupt the OBD processing in
order to send a new command, or as previously
mentioned, to highlight the fact that the ignition has
been turned off. Normally kept at a high level, this
input is brought low for attention, and should remain
so until the Busy line (pin 16) indicates that the
ELM327 is no longer busy, or until a prompt
character is received (if pin 16 is being used for
power control).
This input has Schmitt trigger wave shaping. By
default, pin 15 acts as the RTS interrupt input.
PwrCtrl / Busy (pin 16)
This output pin can serve one of two functions,
depending on how the Power Control options
(PP 0E) are set.
If bit 7 of PP 0E is a ‘1’ (the default), this pin will
function as a Power Control output. The normal state
of the pin will be as set by PP 0E bit 6, and the pin
will remain in that state until the ELM327 switches to
the Low Power mode of operation, when the output
changes to the opposite level. This output is typically
used to control enable inputs, but may also be used
for relay circuits, etc. with suitable buffering. The
discussion on page 84 (‘Modifications for Low Power
Standby Operation’) provides more detail on how to
use this output.
If bit 7 of PP 0E is a ‘0’, pin 16 will function as a
‘Busy’ output, showing when the ELM327 is actively
processing a command (the output will be at a high
level), or when it is idle, ready to receive commands
(the output will be low).
By default, bit 7 of PP 0E is ‘1’, so pin 16 provides
the Power Control function.
RS232Tx (pin 17)
This is the RS232 data transmit output. The signal
level is compatible with most interface ICs (the
output is high when idle), and there is sufficient
current drive to allow interfacing using only a PNP
transistor, if desired.
RS232Rx (pin 18)
This is the RS232 receive data input. The signal
level is compatible with most interface ICs (when at
idle, the level should be high), but can be used with
other interfaces as well, since the input has Schmitt
trigger wave shaping.
VSS (pin 19)
Circuit common must be connected to this pin.
VDD (pin 20)
This pin is the positive supply pin, and should always
be the most positive point in the circuit. Internal
circuitry connected to this pin is used to provide
power on reset of the ELM327 processor, so an
external reset signal is not required. Refer to the
Electrical Characteristics section for further
information.
ISO K (pin 21) and ISO L (pin 22)
These are the active high output signals which are
used to drive the ISO 9141 and ISO 14230 buses to
an active (dominant) level. Many new vehicles do not
require the L Line – if yours does not, you can simply
leave pin 22 open-circuited.
CAN Tx (pin 23) and CAN Rx (pin 24)
These are the two CAN interface signals that must
be connected to a CAN transceiver IC (see the
ELM327DSJ
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www.elmelectronics.com
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Part DetailsOn this page, you can learn information such as the schematic, equivalent, pinout, replacement, circuit, and manual for ELM327 electronic component. |
| Information | Total 30 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
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| Download | [ ELM327.PDF Datasheet ] | |
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