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Don Koch

JTAG-HS3 warm, locks up system

Question

I have a JTAG-HS3 programmer that is performing strangely.

When powered, it seems excessively warm.

I can use it to program my Zynq board if in JTAG boot mode, but it will not boot up unless I disconnect the programmer.  I checked the reset line, and it is not being asserted by the programmer.

I tried a different unit and it works fine.

Is this a common failure mode?

I will be embedding a JTAG-HS3 in my test fixture for the Zynq board.  If I remove power to the programmer, will the JTAG signals be high impedance?  Should I insert buffer gates on TMS, TCK, and TDI to isolate the unit under test from the programmer?

Thanks for your help.

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@Don Koch

Excessive heat suggests that there may be a damaged component on the board.

The reset line is active low and is driven by an open drain buffer that has a 100 ohm series resistor between it and pin 14 of the JTAG connector. There is no onboard pull-up on the reset line and it is assumed that the host board will pull the line to the inactive state (high). When you say reset is not being asserted, do you mean it's always high or always low? Does your board have any push-pull buffers that drive the reset line?

When you say remove power do you mean remove the USB cable or remove VREF from pin 2 of the JTAG header? The onboard buffers will tri-state when they aren't powered. However, the output buffers are powered from the VREF pin of the JTAG header, while the USB controller, which drives the inputs of the output buffers is powered from USB VBUS. If VREF is present but USB power isn't then the buffers will be powered but they should still be held in tri-state because the output enable pin is pulled to ground through a resistor. I don't think you will need to insert extra buffers between TMS, TCK, and TDI.

Thanks,
Michael

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