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JTAG multiple devices

Discussion in 'Embedded' started by amerdsp, Aug 24, 2007.

  1. amerdsp

    amerdsp Guest

    I am new to JTAG and and I am working on a project that that has an
    Atmel AVR. I want to be able to use JTAG but have not bought any
    programming/debugging devices yet. I would like to get something that
    is compatible with other products that I see myself using in the
    future such as FPGAs or other microcontroller families. I am on a
    tight budget and I want to get something that will work with multiple

    Additionally, if all the chips that I use adhere to the IEEE
    standard, one JTAG device should do, right? I may be missing a major
    point and do not understand why is there a plethora of JTAG devices
    that are specific to a certain hardware or software.

    Any help is greatly appreciated.

    Thank you,

    amerdsp, Aug 24, 2007
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  2. amerdsp

    TT_Man Guest

    Not a chance.... Each vendor will have their own software implementation as
    well as their own hardware interface. The only commonality will be the names
    of the signals at the JTAG end....
    TT_Man, Aug 24, 2007
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  3. amerdsp

    Didi Guest

    I may be missing a major
    Because many silicon vendors keep JTAG accessible hardware on their
    chips which goes beyond boundary scan secret; then, they give the
    data some "firm" which is allowed to collect a few thousands per
    sold cable - or do it themselves. The cash they collect on that
    is negligible, but once you give in they have you under control.
    An astonishingly low number of people seem to object paying
    ransoms like that.
    If you can do all you need via boundary scan only, though,
    there should be some cheap way to do it - open source or
    whatever. (I cannot name any because the tols I use have been
    written here and run under DPS which you don't have).

    Didi, Aug 24, 2007
  4. amerdsp

    linnix Guest

    Yes, we object. Especially when we need a few hundred production
    testers and programmers. We don't need stinking Window Point and
    Click either (make no sense in production environments), just connect
    and power it up. We spent hundreds of hours on development (to save
    hundreds of hours in production), but it would still be cheaper
    overall. We make the custom device for less than $10 each.
    Following Atmel specs, we could SPI program the AVR and JTAG boundary
    scan them. We are unable to do JTAG programming as stated in the AVR
    specs. So, we end up with both interfaces on every production board.
    linnix, Aug 24, 2007
  5. amerdsp

    Didi Guest

    Hmm, I did hope you would come in with this sort of a message :).

    I know I am not alone in that - but I think my "astonishingly low"
    still applies...

    Didi, Aug 24, 2007
  6. amerdsp

    amerdsp Guest

    Ok, so if you have different components on your board sharing the same
    JTAG connector, you have to have different JTAG devices as well? And
    you connect which ever JTAG device that corresponds to the chip you
    are testing? Is this how it goes?
    amerdsp, Aug 24, 2007
  7. amerdsp

    linnix Guest

    Yes, we poll the Jtag/Isp IDs and decide how to test/program the board
    linnix, Aug 24, 2007
  8. [Snipped]
    I have had no problem programming Atmel devices using the JTAG
    interface. I use an altera byteblaster and my own software.
    AFAIK there is some sort of issue if the AVR is not the only device on
    the chain, but IIRC it stops one accessing the other devices, and not
    the AVR itself.

    Anton Erasmus
    Anton Erasmus, Aug 25, 2007
  9. amerdsp

    linnix Guest

    Good to know that it could work. I might get back to it later. For
    now, ISP works fine for us. However, it would simplify our interfaces
    if we can do everything in JTAG.
    linnix, Aug 25, 2007
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