ELM327
AT Command Descriptions (continued)
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
a 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.
Another use for this command might be if you
would like to perform a fast initiation with an ISO 9141
type protocol (ie 3 - CARB format). Simply follow these
steps to do that:
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.
AT SP 5
AT FI
AT SP 3
AT BI
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.
and you should be able to then communicate with the
ECU. Note that a protocol close (ie AT PC) is not
required in the above code, as the ELM327
automatically performs one when you switch protocols.
Protocol 5 must be selected to use the AT FI
command, or an error will result.
H0 and H1
[ Headers off or on ]
IFR0, IFR1, and IFR2
[ IFR control ]
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).
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.
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).
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
I
[ Identify yourself ]
Issuing this command causes the chip to identify
itself, by printing the startup product ID string (currently
‘ELM327 v2.0’). Software can use this to determine
exactly which integrated circuit it is talking to, without
having to reset the IC.
ELM327DSI
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