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Thread: CANbus 2-wire to USB adapter

  1. #41
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    Quote Originally Posted by Petrie View Post
    On the OBD2 bus I'm able to log more than 100 parameters per second using multiframe. When I did a road dyno pull to power the Airboy spreadsheet I had to turn down the logging frequency because I could pull responses quicker than the ECU could receive an update of the data (lots of duplicate responses).
    Peter, first of all, I'd like to thank you for your so useful topic...

    I'm using the same CANUSB dongle and found much interesting information in CAN BUS of my mitsubishi galant))

    I can send any single frame with diagnostic request to 7E0... but could you give an example of multi frame request for diagnostic data? and how do I interpret a response frames?

  2. #42
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    Multiframe messages

    There is a big difference between sending multiframe and receiving multiframe.

    I decided to stay away from sending MF requests as they buy you nothing in terms of speed. However, the technique is the same as handling receipts (just the other way around).

    You can send a single frame with many pids (up to 6) and that's simple but you will get a multiframe response which needs to be handled. You can use CanHacker to process MF responses but you need to set it up to do that and it's tricky.

    If you send a full SF request which will result in a MF response then the first frame received will start with a one (1) to indicate this is the first frame of a MF response. You must immediately send a flow control (FC) frame to ask the responder to send the rest of the frames. That means you have sent a total of 2 frames but separated by the FF frame (not together).

    After sending the FC frame you will receive the remainder of the frames (which could be many) and they may not be in the correct order. You must make sure that you put the frames together in the correct order or the message will be corrupt. Asking for the VIN is typical of a SF request that results in a MF response.

    Here's an example of sending a MF message
    http://www.canbushack.com/blog/index...change-the-vin

  3. #43
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    Petrie, thanks for the response!

    using diagnostic requests I found, for example, an engine coolant temperature among broadcast messages... but couldn't identify RPM and vehicle speed? maybe this data has another format or what? how do you think if it's possible that there's no such data in broadcast messages?

  4. #44
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    It is quite possible that both of those items are not on the standard broadcast for the high speed bus.

    There is something else that I should mention. If you have only managed to discover items that have their value expressed in a single byte you may be using the wrong format in CanHacker. Open the detail dialog and you will see that it defaults to Motorola (low byte, high byte). If you switch to Intel (High byte, low byte) you may find the 2 byte values.

    If you have the wrong format, the values are garbage.

  5. #45
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    Quote Originally Posted by midiser View Post
    Petrie, thanks for the response!

    using diagnostic requests I found, for example, an engine coolant temperature among broadcast messages... but couldn't identify RPM and vehicle speed? maybe this data has another format or what? how do you think if it's possible that there's no such data in broadcast messages?
    hello midiser,
    I found the same situation, looking at broadcast messages on a subaru. Engine coolant is broadcast, but not engine rpm and vehicle speed.
    I expected all 3 to be broadcast, as the PCM (eng coolant, eng rpm), ABS module (wheel speed / vehicle speed) and BIU (instrument combination meter) are all on the CAN bus.
    It appears eng coolant temp data goes to the instruments via the bus, but rpm and vehicle speed data is transmitted in another manner.
    rpm and vehicle speed can be obtained by making an obd request.

  6. #46
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    guys, thanks a lot for your responses..

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