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Question: To disable the TAP controller, TCK must be tied LOW (VSS) to prevent clocking of the device. If tie high is the same, pull up, just not leave it float.
There are no internal pull downs for the TCK. The pin can be left floating; however we do not recommend it. TCK can be tied high; however, it is not a usual practice. Our recommendation would be to tie TCK low for disabling the JTAG. This is a recommendation as per IEEE specifications.