I have the UCD90160A power sequencer in a JTAG chain.
However I am having some problems getting it to report its ID code when scanning the chain.
I can confirm it is going into JTAG mode, as the PMBUS address changes to 126 and I can see IDCODE from downstream devices proving at least TDI and TDO are working. I can't easily cofirm TMS is getting to the device. TCK must be as data is being clocked through.
One thought was that TRST is permantly pulled low via 10K resistor. Does this need to be driven high to further enable the JTAG interface?
Is there another way through toggling TMS and TCK to get the device to reset the JTAG TAP controller so that is reports its IDCODE?