Understanding JTAG

Discussion in 'Embedded Systems and Microcontrollers' started by Bosparra, Sep 8, 2010.

  1. Bosparra

    Thread Starter Member

    Feb 17, 2010
    79
    3
    I've been playing with Atmel's AVR range of microcontrollers for a while now. I recently got my hands on the AT90USBKEY evaluation board, what a neat little toy!

    Anyway, this board is equipped with a JTAG interface. I have never used JTAG before, but I have done quite a bit of research on JTAG and understand what it is for, but I can't seem to find a reasonably priced JTAG dongle that supports this particular device. Ideally, I would like to build one.

    I have a few questions to get a better understanding of JTAG in general:
    1. It appears that the implementation of the JTAG interface on a particular device, is proprietry i.e. there is no software standard?
    2. Am I right in saying that the JTAG spec only defines the electrical interface?
    3. If my assumptions are right so far, does it mean that I have to get a new JTAG dongle or dongle firmware everytime a new, as yet unsupported device comes out?
    4. If my assumptions are incorrect, does anyone know of a JTAG dongle solution that has source code available?
     
  2. Bosparra

    Thread Starter Member

    Feb 17, 2010
    79
    3
    Is there no one around that knows anything about JTAG?
     
  3. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    To many of us mortal the JTAG is just a means to program and debug the AVR.

    A single JTAG interface dongle will interface between your PC and the AVR and allows AVRStudio to communicate with the device.

    It will probably works with all AVR chips which has a JTAG interface/port.
     
  4. Bosparra

    Thread Starter Member

    Feb 17, 2010
    79
    3
    Thanks for that eblc1388, I understand that. My questions relate to the level 'openness' of the interface.
     
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