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TAP Control signals

Leo1008

 

Hi,

I read that the TAP state machine generates control signals like Clock_IR, Shift_IR, Update_IR, Clock_DR, Shift_DR and Update_DR.

Out of these I could figure, if I'm not wrong, that the shift and update control signals would be asserted upon reaching the corresponding state in the state machine.
However I'm not quite sure when the Clock_DR/IR control signal would be asserted. Would it be before entering the capture state or while in the capture state??

Thanks

Insiya
  • Andy Hughes

     Insiya,

        The control signals generated by the RTL-Compiler JTAG controller all conform to the 1149.1 standard.  All control signals are generated based on specific states and state transitions.  Clock-DR and Clock-IR clock pulses are generated during different states.  For instance, Clock-DR pulses are generated in the Capture-DR and in Shift-DR state along with the Exit2-DR state.  Same goes for Clock-IR.  

      My question is, what are you really trying to figure out by understanding this clocking?  With standard boundary scan cells all of the timing and execution of the 1149.1 tests are taken care of by the controller.  Are you trying to do something else with this clocking outside of the 1149.1 standard?

     

    Andy Hughes

    Core Comp Architect

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