ELM325 데이터 시트보기 (PDF) - Elm Electronics

부품명

상세내역

제조사

ELM325

J1708 Interpreter

Elm Electronics 

AT Command Descriptions

The following describes each AT Command that the

current version of the ELM325 supports, in some

detail. Many of these commands are also described

further in other sections:

ELM325

<CR>

[ repeat the last command ]

Sending a single carriage return character causes

the ELM325 to repeat the last command that it

performed. This helps if you wish to repeat a request

several times to obtain updates for a monitored value,

for example.

AF0 and AF1

[ Auto Formatting off or on* ]

All messages must start with the sender’s address

(the MID) and end with a checksum. If automatic

formatting is on (it is by default), the ELM325 will add

these to every message for you, so that you only need

to provide the data bytes that you wish to send. If

automatic formatting is off, you must provide all bytes,

including the MID and the checksum.

Automatic (ie ‘auto’) formatting also provides help

when making requests for a PID. If you provide one

data byte, or two data bytes with the first being 01, the

ELM325 assumes that you wish to make a PID

request. It will add the MID, the request PID,

checksum, etc. for you, set the filters if you haven’t,

and send the request. If the auto formatting is off, all

bytes that you provide are sent without modification of

any kind (but the ELM325 still attempts to set filters for

you, if you have not set any).

One final issue to note is that the ELM325’s

internal J1708 buffer is 21 bytes long. This means that

you may actually send a 23 byte message if formatting

is on (MID + 21 bytes in buffer + checksum), but if the

auto formatting is off, the total length of the message

must be 21 bytes or less (as the entire message is

taken from the buffer). It also means that if you try to

provide 21 data bytes for a message, plus a message

count nibble, you will get an error (as you have over-

filled the internal buffer). This is generally of no

concern if you are implementing the SAE J1587

protocol, but may be an issue if you are trying to send

some special SAE J1922 messages.

C0 and C1

[ Checksum display off* or on ]

These commands are used to make the received

checksum byte visible or not. Usually, it is preferred

that the byte not be shown, so the ELM325 hides it by

default. If you wish to see the byte printed with every

message, simply send AT C1.

D

[ set all to Defaults ]

This command is used to set the options to their

default (or factory) settings, as when power is first

applied. Any settings that you had made for a custom

MID, for filters, for message formatting, or timer

settings will be restored to their default values.

E0 and E1

[ Echo off or on* ]

These commands control whether or not the

characters received on the RS232 port are echoed

(retransmitted) back to the host computer. Character

echo can be used to confirm that the characters sent

to the ELM325 were received correctly. The default is

E1 (or echo on).

EM0 and EM1

[ Error Messages off or on* ]

If a message is received and there is a problem

with it, the ELM325 will add an error description to the

received line. An arrow (‘<‘) that points to the message

is printed first, then either PROT ERROR, RX ERROR,

or DATA ERROR is printed to describe the problem.

You may find that the description is of little use to you

in your application, and wish to only see the ‘arrow’. If

you set AT EM0, the ELM325 will do that for you.

F1

[ reset Filter 1 ]

If you have set message receive filter F1 and wish

to disable that setting, simply send AT F1. The

ELM325 will discard any setting that you had made.

F2

[ reset Filter 2 ]

If you have set message receive filter F2 and wish

to disable that setting, simply send AT F2. The

ELM325 will discard any setting that you had made.

ELM325DSA

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

8 of 31

Share Link: