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JTAG Emulators/ Debuggers

Discussion in 'General Electronics' started by Ankur Kashyap, Aug 11, 2004.

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  1. hi

    I'm working on ARM 7 based microcontroller. JTAG is now in every
    chip...whether uCon,FPGA,DSP...ect.I would like to know what is JTAG
    interface, how it works, pinout, how does emulators/ debugger with
    JTAG work, while running the the microcontroller sends
    signals thru JTAG interface to debuggers...

  2. Ken Smith

    Ken Smith Guest

    There are a few logic lines:

    TMS = Test mode select
    TDI = Test data in
    TDO = Test data out
    TCK = Test clock

    Inside the chip is a state machine and some shift registers.

    Using TDI and TCK you shift bits into the various flip-flops inside. Some
    of these flip-flops are grouped together into what is called a command
    register. By setting the command register to different values, you cause
    different things to happen.

    The JTAG standard specifies some of these commands and some others are
    defined by the maker of the chip.

    Debuggers generally work with the commands the maker added. The chip
    being debugged actually has most of the debugging circuits built into it.
    The JTAG interface is just a way to get data to and from this hardware.
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