Spark Logic

ELM327 OBD interpreter IC connection guide

ELM327 OBD interpreter IC SOIC-28 wiring guide with power, signal assignments, and bench checks.

PDIP-28 28 contacts

SOIC-28

28 contacts Current package

Elm Electronics · 7.50 mm nominal body width

Power the IC and strap unused inputs

Required

Use a regulated 5 V supply and both VSS contacts. Fit the crystal and bypass capacitors. Strap the unused inputs to defined levels. Pin 6 is low to force 9600 bit/s.

4.000 MHz between Crystal input and Crystal outputCrystal input4.000 MHzCrystal output
27 pF typical, match crystal between Crystal input and ReturnCrystal input27 pF typical, match crystalReturn
27 pF typical, match crystal between Crystal output and ReturnCrystal output27 pF typical, match crystalReturn
100 nF between 5 V supply and Return5 V supply100 nFReturn
10 kΩ between 5 V supply and UART receive idle5 V supply10 kΩUART receive idle

Bench checks

  • Check the rail and both ground leads before inserting the IC.
  • Verify the clock circuit and keep every unused input at the documented high or low level.

Elm Electronics ELM327DSK, pp. 1 and 4–7

Connection scenarios

Read the chip identity over UART

Power off, then cross the UART data lines with a 5 V logic adapter. Keep the 10 kΩ pull-up on the receiver and leave the vehicle interfaces disconnected.

Bench checks

  • Open the serial port at 9600 bit/s, 8N1, no flow control.
  • Send ATI followed by carriage return and check the identification string and prompt.

ELM327DSK, Communicating with the ELM327 and AT I command.

SOIC-28 wiring map

Highlighted contacts are used in the required step or selected circuit. Select a contact to inspect it.

Top view · Pin 1 at upper left · Schematic outline
Selected pin details

6 · Baud Rate

Input · Control

Low selects 9600 bit/s. High uses PP 0C, normally 38400 bit/s at factory settings.

Elm Electronics ELM327DSK, pp. 1 and 4–7

Electrical limits · Pin in the reference

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.