The design block in question is generated by Quartus, it is the shift register megafunction. When I simulate the design I find that some of the signals do not show 0 or 1, rather they show different expression for value: enter image description here

Where is says Pu0, these are connected to logic 0 permanently. Where it says St0, that is driven low and where it says St1 that is driven high, but not permanently. Why do I see this instead of 0 or 1?


I am myself a beginner so this won't answer your question entirely, but maybe you can look at this table from User's manual

Table: table

P.S. I also realize this is an old post, but anyway, whoever lands on this page might find this info useful.

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