ELM327P datasheet(24/76 Pages) ELM

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ELM327

ELM327DSH

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AT Command Descriptions (continued)

3 - ISO 9141-2 (5 baud init, 10.4 kbaud)

4 - ISO 14230-4 KWP (5 baud init, 10.4 kbaud)

5 - ISO 14230-4 KWP (fast init, 10.4 kbaud)

6 - ISO 15765-4 CAN (11 bit ID, 500 kbaud)

7 - ISO 15765-4 CAN (29 bit ID, 500 kbaud)

8 - ISO 15765-4 CAN (11 bit ID, 250 kbaud)

9 - ISO 15765-4 CAN (29 bit ID, 250 kbaud)

A - SAE J1939 CAN (29 bit ID, 250* kbaud)

B - USER1 CAN (11* bit ID, 125* kbaud)

C - USER2 CAN (11* bit ID, 50* kbaud)

* default settings (user adjustable)

The first protocol shown (0) is a convenient way of

telling the ELM327 that the vehicle’s protocol is not

known, and that it should perform a search. It causes

the ELM327 to try all protocols if necessary, looking for

one that can be initiated correctly. When a valid

protocol is found, and the memory function is enabled,

that protocol will then be remembered, and will

become the new default setting. When saved like this,

the automatic mode searching will still be enabled, and

the next time the ELM327 fails to connect to the saved

protocol, it will again search all protocols for another

valid one. Note that some vehicles respond to more

than one protocol - during a search, you may see more

than one type of response.

ELM327 users often use the AT SP 0 command to

reset the search protocol before starting (or restarting)

a connection. This works well, but as with any Set

Protocol command, it involves a write to EEPROM,

and an unnecessary delay (of about 30 msec) while

the write occurs. Beginning with v1.3 of the ELM327, a

write to EEPROM will no longer be performed for an

SP 0 (or an SP A0, or SP 0A) command, but the

command will still reset the protocol to 0 for you. If you

really want to change what is stored in the internal

EEPROM, you must now use the new AT SP 00

command.

If another protocol (other than 0) is selected with

this command (eg. AT SP 3), that protocol will become

the default, and will be the only protocol used by the

ELM327. Failure to initiate a connection in this

situation will result in a response such as ‘BUS INIT:

...ERROR’, and no other protocols will be attempted.

This is a useful setting if you know that your vehicle(s)

only require the one protocol, but also one that can

cause a lot of problems if you do not understand it .

SP Ah

[ Set Protocol to Auto, h ]

This variation of the SP command allows you to

choose a starting (default) protocol, while still retaining

the ability to automatically search for a valid protocol

on a failure to connect. For example, if your vehicle is

ISO 9141-2, but you want to occasionally use the

ELM327 circuit on other vehicles, you might use the

AT SP A3 command, so that the first protocol tried will

then be yours (3), but it will also automatically search

for other protocols. Don't forget to disable the memory

function if doing this, or each new protocol detected

will become your new default.

SP Ah will save the protocol information even if

the memory option is off, except for SP A0 and SP 0A

which as of v1.3 no longer performs the write (if you

need to change the EEPROM, use SP 00). Note that

the ‘A’ can come before or after the h, so AT SP A3

can also be entered as AT SP 3A.

SR hh

[Set the Receive address to hh ]

Depending on the application, users may wish to

manually set the address to which the ELM327 will

respond. Issuing this command will turn off the AR

mode, and force the IC to only accept responses

addressed to hh. Use caution with this setting, as

depending on what you set it to, you may accept a

message that was actually meant for another module,

possibly sending an IFR when you should not. To turn

off the SR filtering, simply send AT AR.

This command has limited use with CAN, as it only

monitors one byte of the ID bits, and that is not likely

selective enough for most CAN applications (the CRA

command may be a better choice). Also, the command

has no effect on the addresses used by the J1939

protocols, as the J1939 routines set their own receive

addresses based on the ID bit (header) values.

This SR command is exactly the same as the RA

command, and can be used interchangeably with it.

Note that CAN Extended Addressing does not use this

value - it uses the one set by the AT TA command.

[ use the Standard Sequence for searches ]

SAE standard J1978 specifies a protocol search

order that scan tools should use. It follows the number

order that we have assigned to the ELM327 protocols.

In order to provide a faster search, the ELM327 does

not normally follow this order, but it will if you

command it to with AT SS.

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