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Observer mogarfield
Registered: ‎08-08-2017

ARM_DAP is missing

Hi guys,

We made two boards based on ZYNQ and they are not able to connect to the ARM_DAP. We check all the voltages, clk waveform, boot setting, power and reset sequencing, PCB design, Vivado version, and they seem all right.

But when we use a capacitor or a probe of WaveRunner to touch on the pin of PS_clk, the Vivado is able to detect the ARM_DAP. After detection, the capacity or a probe of WaveRunner can be removed and the system goes well.

Further, we try to increase the decouple capacity for the power of oscillator which provides PS_clk , and find it's no help. It has already been 0.1uf. And the trace of PS_clk is very short and close to the pad, with ground shield and 50-ohm characteristic resistance. 

Anyone knows why?


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1 Reply
Xilinx Employee
Xilinx Employee
Registered: ‎09-04-2012

Re: ARM_DAP is missing

I know that you mentioned that you looked at the power ramps, sequencing, reset, and clock but I would still suspect that it is related to either:

  • Power sequencing
  • Stable clock relationship to reset deasserted
  • Power/ground rail noise
  • Stable reset relationship to power ramp
  • Stable clock relationship to power ramp
  • Some noise on the JTAG signals during power ramp

Double-check these against the datasheet specifications.



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