I have a design with a differential clock port "sys_clk_p" that has "IO-Standard" set to "LVDS".
In the Vivado IDE I see "DIFF_TERM_ADV" has a value of "TERM_NONE" in the "I/O Ports" tab for the clock input "sys_clk_p".
However, when I run the following command in the Tcl console, I get an empty value:
get_property DIFF_TERM_ADV [get_ports sys_clk_p]
I would expect the Tcl command to show a value of "TERM_NONE" instead of being empty.
Why is there a difference in output between the GUI and Tcl?
This is due to a general difference between how the Vivado IDE and the underlying Vivado "engine" establish and display default values.
In spite of the difference in displayed values, at bitstream, all default values will be handled appropriately.
Values are shown this way in the GUI to let the user know that they do not need to set every property of a port when it is not required.