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Thread: Sending Multiline Messages with an ELM327

  1. #1
    Constant Bitrate
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    Sending Multiline Messages with an ELM327

    Is there a best-practice for sending multiline messages using an ELM327?

    I know it does the flow-control for receiving multiline messages automatically, but I can't find any reference to whether it might also do this automatically for sending.

    I'd be curious if anyone has any advice on this. I'm aware of other threads and doing this manually according to 15765-2, which of course we can do, but I thought the ELM might have made life a little simpler than that.



    Lukeyson

  2. #2
    Newbie
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    Oct 2010
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    could you please give an example of at commands how to set elm327 for multi frame iso15765?
    thank

  3. #3
    VENDOR - ScanTool Vitaliy's Avatar
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    Quote Originally Posted by raedbenz View Post
    could you please give an example of at commands how to set elm327 for multi frame iso15765?
    thank
    There isn't a straightforward way to do this. You can hack it as follows:

    1. Set up CAN filters to accept flow control frames.
    2. Turn off CAN autoformatting (ATCAF0).
    3. Send the first frame, specifying that you are expecting one response.
    4. Receive the flow control frame.
    5. Send the rest of the frames, this time specifying that you are expecting zero responses.


    Note that you must do this under program control (you can't do it "by hand") because of the timeouts.

    We may enable sending of multi-frame responses in OBDLink, in the next release. The way it would work, is if you try to send a message in excess of 8 bytes, it will be automatically split up into multiple frames (this already works in ECUsim, which uses the same software CAN module).

    Vitaliy

    PS If this is a commercial project, send me a private message ([email protected]).
    OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
    Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

    You cannot send me a private message using this forum. Use my email instead: vitaliy[@]scantool.net.

  4. #4
    Newbie
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    Oct 2010
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    hello,

    Thanks fr your reply..
    what about receiving multi frames? would you send the flow control manually or you let elm327 to send it automatically using ATCFC1??

    thanks

  5. #5
    VENDOR - ScanTool Vitaliy's Avatar
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    ELM327 can receive multiframe messages out of the box. There is a caveat, however: it has a rather shallow receive buffer and under certain conditions, it overflows. In most cases, this can be overcome by switching to higher baud rates on the PC side.
    OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
    Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

    You cannot send me a private message using this forum. Use my email instead: vitaliy[@]scantool.net.

  6. #6
    Newbie
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    Oct 2010
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    Hello,

    i wrote a little program to send/receive this CAN message:
    Code:
    5FB 1A 91 : 6FB 5A 91 39 39 37 36 31 30 31 30 37 30 33;
    AutoFormatting is OFF and FlowControl is OFF.
    That's what the does:
    Code:
    send:
    5FB 02 1A 91 00 00 00 00 00
    read:
    6FB 10 0D 5A 91 39 39 37 36
    send:
    5FB 30 10 05 00 00 00 00 00
    read:
    NOTHING...
    My concern is timeouts. what is a recommended elm327 timeout. also how fast the FC should be sent after getting the first frame??
    any hints??

    Thanks

  7. #7
    Newbie
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    Jun 2013
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    I'm stuck at the first and third points -->> Set up CAN filters to accept flow control frames, -->> Send the first frame, specifying that you are expecting one response.
    can u please tell what commands to use? i'm trying to send 5 multiline commands but pcan device shows that the data is not being sent the way I want... I haven't understood the above mentioned points so i'm just skipping them. how do you specify that you are expecting one response?

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