ELM325 데이터 시트보기 (PDF) - Elm Electronics

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ELM325

J1708 Interpreter

Elm Electronics 

ELM325

Sending AT Commands

Before learning some J1587 Commands, we will

show a few examples of how to use an AT Command.

We will assume that you have built (or purchased) a

circuit that is similar to that of Figure 7 in the Example

Applications section.

Do not connect your circuit to a vehicle at this

time. Power it from a test source only (a 9V ‘transistor

radio’ battery works well), and connect it to your PC as

discussed in the Communicating with the ELM325

section.

For your first command, simply reset the IC by

sending AT Z. Try this a few ways (don’t forget to

press enter or return after each):

>AT Z

or

>atz

or

>a T z

You should see the RS232 LEDs blink as you type

each letter, and after you press return (or enter) you

should see all four Tx/Rx LEDs blink, in order, followed

by a final blink of the RS232 Tx LED as the ELM325

sends ‘ELM325 v1.0’.

Most J1708 messages are continually sent on the

data bus, at a predetermined rate. Some messages

may be sent 10x per second, while others are only 1x

per 10 seconds. This means that you may need to

adjust the internal timeout setting depending on what

message you are attempting to receive. We will adjust

this timeout setting next.

Try this request for trouble codes:

>AT TC

After about 2 seconds, you should see a response

that looks like:

NO DATA

>

since there is no vehicle attached, there was no data

received.

Now, adjust the timeout to 10 seconds. If you look

at the AT command list, you will see that there is a Set

Timeout command that is used for this. Timing is in

increments of 100 msec (0.1 sec), so to obtain a 10

second delay, the AT ST setting should be 100. We

need to convert the 100 to hexadecimal, however, as

all numbers handled by the ELM325 must be in

hexadecimal. Converting then, 100 (= 6 x 16 + 4) is 64

in hexadecimal, so we send:

>AT ST 64

Again, don’t forget to press return (or enter). Now,

the timeout should be set to 10 seconds. To verify this,

repeat the Trouble Codes command:

>AT TC

It should be 10 seconds before you see the NO

DATA response this time. To try it again, you do not

need to enter the AT TC command again, you only

need to press enter, and the ELM325 will repeat your

last command (AT TC) for you.

As a final test, enter AT TC again, but before the

10 seconds is up, press any key on the keyboard. You

should see the ELM325 respond with:

STOP?

which means that it was interrupted and it thinks that

you wish to stop. If you ever see the ‘STOP?’

response, it means that the ELM325 thinks it has been

interrupted by you.

Now, restore the AT ST time to the default value,

with the Defaults command:

>AT D

You should see a response of ‘OK’ and then a

prompt character on a new line, to show that the

ELM325 is waiting for you. In this case, you might also

have sent AT ST 00, since that also restores the

timeout setting to its default value.

Experiment with these commands – you are not

connected to a vehicle, so can do no harm. Sending

AT Commands is not difficult, they just require a little

practice.

ELM325DSA

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

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