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ELM327

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ELM327DSC

Ordering Information

These integrated circuits are 28 pin devices, available in either a 300 mil wide plastic (‘skinny’) DIP format or in a

300 mil SOIC surface mount type of package. To order, add the appropriate suffix to the part number:

300 mil 28 pin Plastic DIP..............................ELM327P

300 mil 28 pin SOIC....................................ELM327SM

ISO In (pin 12)

This is the active low input for the ISO 9141 and

ISO 14230 data signal. It is derived from the K Line,

and should be at a high logic level when at rest (bus

recessive). No special amplification is required, as

this input has Schmitt trigger waveshaping.

PWM In (pin 13)

This is the active low input for the J1850 PWM data

signal. It should normally be at a high level when at

rest (ie. bus recessive). This input has Schmitt

trigger waveshaping, so no special amplification is

required.

J1850 Bus- (pin 14)

This active high output is used to drive the J1850

Bus- Line to an active (dominant) level for J1850

PWM applications. If unused, this output can be left

open-circuited.

RTS (pin 15)

This active low “Request To Send” input can be used

to interrupt the OBD processing in order to send a

new command. Normally high, the line is brought low

for attention, and should remain so until the Busy

line (pin 16) indicates that the ELM327 is no longer

busy. This input has Schmitt trigger waveshaping.

Busy (pin 16)

This active high output shows the current state of the

ELM327. If it is at a low level, the processor is ready

to receive ASCII commands and characters, but if it

is at a high level, commands are being processed.

RS232Tx (pin 17)

This is the RS232 data transmit output. The signal

level is compatible with most interface ICs (output is

normally high), 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 is normally high), but can be used with

other interfaces as well, since the input has Schmitt

trigger waveshaping.

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 microprocessor, 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 transeiver IC for proper

operation. If you are connecting to an existing CAN

system, the integrity of the entire system might be

jeopardized if a proper interface is not used. See the

Example Applications section for more information.

RS232 Rx LED (pin 25), RS232 Tx LED (pin 26),

OBD Rx LED (pin 27) and OBD Tx LED (pin 28)

These four output pins are normally high, and are

driven to low levels when the ELM327 is transmitting

or receiving data. Current capability is suitable for

directly driving most LEDs through current limiting

resistors, or interfacing to other logic for status

reporting. If unused, these pins should be left open-

circuited.

Pin Descriptions (continued)

ELM327P 数据表(PDF) 3 Page - ELM Electronics

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