ELM327 OBD interpreter IC pinout · SOIC-28

SOIC-28 pinout

Top view · Pin 1 at upper left · Schematic outline

Selected pin details

21 · ISO K

Output · Outputs

Drive signal for an external K-line interface.

Elm Electronics ELM327DSK, pp. 1 and 4–7

Electrical limits · Link to this pin

All 28 pins

Pin	Signal	Direction	Function
1	MCLR Input	Input	Active-low reset. Hold high when unused.
2	Vmeasure Analog input	Analog input	Voltage measurement input. The signal must remain between VSS and VDD.
3	J1850 Volts Output	Output	Selects the external J1850 driver supply for PWM or VPW.
4	J1850 Bus+ Output	Output	Control output for the external positive J1850 line driver.
5	Memory Input	Input	High enables the protocol-memory default at startup.
6	Baud Rate Input	Input	Low selects 9600 bit/s. High uses PP 0C, normally 38400 bit/s at factory settings.
7	LFmode Input	Input	Sets the default response terminator. High adds a line feed after carriage return.
8	VSS Return	Return	Connect to the supply return.
9	XT1 Oscillator input	Oscillator input	Connect one side of a 4.000 MHz crystal and its load capacitor.
10	XT2 Oscillator output	Oscillator output	Connect the second crystal terminal and its load capacitor.
11	VPW In Input	Input	Conditioned receive input for J1850 VPW.
12	ISO In Input	Input	Conditioned receive input for ISO 9141 and ISO 14230.
13	PWM In Input	Input	Conditioned receive input for J1850 PWM.
14	J1850 Bus− Output	Output	Control output for the external negative J1850 line driver.
15	IgnMon / RTS Input	Input	Ignition-monitor or request-to-send input. Hold high when unused.
16	PwrCtrl / Busy Output	Output	Power control by default. PP 0E can select the command-busy function.
17	RS232Tx Logic output	Logic output	UART transmit, high when idle. A bipolar RS-232 port needs a separate transceiver.
18	RS232Rx Logic input	Logic input	UART receive, high when idle. This pin has Schmitt-trigger input levels.
19	VSS Return	Return	Connect to the supply return.
20	VDD Supply input	Supply input	Nominal 5 V supply. Place a bypass capacitor close to the part.
21	ISO K Output	Output	Drive signal for an external K-line interface.
22	ISO L Output	Output	Drive signal for an external L-line interface.
23	CAN Tx Output	Output	Transmit logic output to a separate CAN transceiver.
24	CAN Rx Input	Input	Receive logic input from a CAN transceiver. Hold high when unused.
25	RS232 Rx LED Output	Output	Active-low activity output. Fit a current-limiting resistor if driving an LED.
26	RS232 Tx LED Output	Output	Active-low activity output. Fit a current-limiting resistor if driving an LED.
27	OBD Rx LED Output	Output	Active-low activity output. Fit a current-limiting resistor if driving an LED.
28	OBD Tx LED Output	Output	Active-low activity output. Fit a current-limiting resistor if driving an LED.

Signal assignments

Host UART

Use compatible 5 V logic or a level converter. The name RS232 on these pins describes the serial link function.

CAN transceiver interface

Use a separate CAN transceiver for connection to CANH and CANL. Pin 24 is held high in the bench setup.

ISO diagnostic interface

These are logic pins for the external interface circuit in the manufacturer example.

SAE J1850 interface

Use the external line drivers and receiver circuits for the selected bus.

Electrical limits

Parameter	Limit	Conditions and source
VDD operating range4.2–5.5 V	4.2–5.5 V	5 V nominal for this ELM327. ELM327L is specified separately. Elm Electronics ELM327DSK, pp. 1 and 4–7
Crystal4.000 MHz	4.000 MHz	27 pF is the manufacturer example for each load capacitor. Follow the chosen crystal specification. Elm Electronics ELM327DSK, pp. 1 and 4–7
UART baud strap9600 bit/s with pin 6 low	9600 bit/s with pin 6 low	The bench guide uses 8N1 with no flow control. Elm Electronics ELM327DSK, pp. 1 and 4–7

Models and documents

This reference covers the Elm Electronics 5 V ELM327 and its two 28-lead packages. The companion verifies host UART operation on the bench with no vehicle connected.

ELM327SM: Surface-mount option.

Elm Electronics ELM327 datasheet· ELM327DSK, pinout, input termination, UART commands and package drawings.