ELM327P datasheet(16/76 Pages) ELM

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which blocks subsequent searching through CAN

protocols if PP 2A bit 5 is ‘1’. Normally, an event such

as this will affect all searches until the next power off

and on, but it can be ‘forgotten’ using software, with

the AT FE command.

Another example is an ‘LV RESET’ event which

will prevent searches through CAN protocols if PP 2A

bit 4 is ‘1’. It may also be forgotten with the AT FE

command.

[ perform a Fast Initiation ]

One version of the Keyword protocol (the ELM327

protocol 5) uses what is known as a fast initiation

sequence to begin communications. Usually, this

sequence is performed when the first message needs

to be sent, and then the message is sent immediately

after. Some ECUs may need more time between the

two

however,

and

having

separate

initiation

command allows you to control this time. Simply send

AT FI, wait a little, then send the message. You may

need to experiment to get the right amount of delay.

Protocol 5 must be selected to use the AT FI

command, or an error will result.

H0 and H1

[ Headers off or on ]

These commands control whether or not the

additional (header) bytes of information are shown in

the responses from the vehicle. These are not

normally shown by the ELM327, but may be of interest

(especially if you receive multiple responses and wish

to determine what modules they were from).

Turning the headers on (with AT H1) actually

shows more than just the header bytes – you will see

the complete message as transmitted, including the

check-digits and PCI bytes, and possibly the CAN data

length code (DLC) if it has been enabled with PP 29 or

AT D1. The current version of this IC does not display

the CAN CRC code, nor the special J1850 IFR bytes

(which some protocols use to acknowledge receipt of a

message).

[ Identify yourself ]

Issuing this command causes the chip to identify

itself, by printing the startup product ID string (currently

‘ELM327 v1.4b’). Software can use this to determine

exactly which integrated circuit it is talking to, without

having to reset the IC.

IB 10

[ set the ISO Baud rate to 10400 ]

This command restores the ISO 9141-2 and

ISO 14230-4 baud rates to the default value of 10400.

IB 48

[ set the ISO Baud rate to 4800 ]

This command is used to change the baud rate

used for the ISO 9141-2 and ISO 14230-4 protocols

(numbers 3, 4, and 5) to 4800 baud, while relaxing

some of the requirements for the initiation byte

transfers. It may be useful for experimenting with some

vehicles. Normal (10,400 baud) operation may be

restored at any time with the IB 10 command.

IB 96

[ set the ISO Baud rate to 9600 ]

This command is used to change the baud rate

used for the ISO 9141-2 and ISO 14230-4 protocols

(numbers 3, 4, and 5) to 9600 baud, while relaxing

some of the requirements for the initiation byte

transfers. It may be useful for experimenting with some

vehicles. Normal (10,400 baud) operation may be

restored at any time with the IB 10 command.

IFR0, IFR1, and IFR2

[ IFR control ]

The SAE J1850 protocol allows for an In-Frame

Response (IFR) byte to be sent after each message,

usually to acknowledge the correct receipt of that

message. The ELM327 automatically generates and

sends this byte for you by default, but you can override

this behaviour with this command.

The AT IFR0 command will disable the sending of

all IFRs, no matter what the header bytes require.

AT IFR2 is the opposite - it will cause an IFR byte to

always be sent, no matter what the header bytes say.

The AT IFR1 command is the default mode, with the

sending of IFRs determined by the ‘K’ bit of the first

header byte (for both PWM and VPW).

IFR H and IFR S

[ IFR from Header or Source ]

The value sent in the J1850 In-Frame Response

(IFR) byte is normally the same as the value sent as

the Source (or Tester) Address byte that was in the

header of the request. There may be occasions when

it is desirable to use some other value, however, and

this set of commands allows for this.

If you send AT IFR S, the ELM327 will use the

value defined as the Source Address (usually F1, but it

can be changed with PP 06), even if another value

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AT Command Descriptions (continued)

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