5 of 11

ELM634

ELM634DSB

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

Remember that they are not case-sensitive, they can

have spaces or tab characters embedded as you wish,

and that for the on/off type commands, the ‘0’

character is the number zero.

AT Commands (continued)

BR

[ display the Baud Rate ]

This command asks the IC for the LIN baud rate it is

currently operating at. The ELM634 only supports

one baud rate, so this command will always return

with the response ‘9600’.

D

[ set all to Defaults ]

This command resets all of the options to their

default values which were set at the last power-up,

or manual reset command. This usually only affects

the echo and linefeed modes, but if the RS232Rx

pin was at an active level during the last reset, the

IC will immediately enter the Monitor All (AT MA)

mode after this command is issued.

E0 and E1

[ Echo off(0) or on(1) ]

These commands control whether or not characters

received on the RS232 port are re-transmitted (or

echoed) back to the host computer. To reduce traffic

on the RS232 bus, users may wish to turn echoing

off by issuing AT E0. The default is E1 (echo on).

I

[ Identify yourself ]

Issuing this command causes the chip to identify

itself, by printing the startup product ID string (which

is currently ‘ELM634 v2.0’). Software can use this to

determine exactly which integrated circuit it is talking

to, without resorting to resetting the entire IC.

L0 and L1

[ Linefeeds off(0) or on(1) ]

The option of transmitting a linefeed character after

each carriage return character is controlled by these

commands.

If

an

AT

L1

is

issued,

linefeed

generation will be turned on, and for AT L0, it will be

off. Users may wish to have this option on if using a

terminal program, but off if using a custom interface

(as the extra characters serve no real purpose in

such a case). The default setting is L1 (linefeed

characters are sent after every carriage return).

MA

[ Monitor All ]

This command causes the IC to immediately begin

monitoring the LIN bus for messages, displaying all

that it finds. It can be interrupted at any time by

activity on the RS232 receive input.

MR hh

[ Monitor for a Response to hh ]

This is a special version of the AT MA command.

Only identifier/command bytes matching the hex

characters ‘hh’ will be displayed, and all others will be

ignored. This can be useful if trying to track down a

troublesome switch problem, or for triggering another

action on a specific input.

Z

[ reset all ]

This combination causes the chip to perform a

complete reset, as if power was cycled off and then

on again. All settings are returned to their default

values, and if the RS232Rx input is not held at an

active level for the entire reset time, the chip will be

put in the idle state, waiting for characters to arrive

on the RS232 bus. Note that the level at the Rxmode

input is measured again at this time, so the RS232Rx

input may be affected if the level at pin 4 has

changed since the initial power-up.