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Thread: Lenght data bytes in VPW, ISO9141-2, PWM or KWP2000

  1. #1
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    Lenght data bytes in VPW, ISO9141-2, PWM or KWP2000

    Hi everyone!! I am building my own ECU simulator.

    For VPW, ISO9141-2, PWM or KWP2000, is it necessary to indicate in the requests and responses the length of useful data bytes like in CAN protocol?

    For example in CAN, a frame is: 7DF 8 02 01 01 00 00 00 00 00 where 02 indicates the length of useful data bytes (01 01)

    How is it in these protocols?

    Thanks!!

  2. #2
    VENDOR - ScanTool Vitaliy's Avatar
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    I'm surprised that you are building an ECU simulator without access to essential protocol documentation.

    VPW, ISO, and PWM frames do not include a data length byte, but KWP does.

    The "02" in your example is a "PCI byte", it's not a simple data length field.

    Vitaliy
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