vhdl and unknown values

[krpz]

Hello, i have a question about vhdl and unknown values,

I wonder if in structural vhdl we need to write some extra code in order to deal with unknown values.For example in this piece of code:

Agt <= (a and pr_a)or (a and (not b)) or ((not b) and pr_a);

i read somewhere that the and, or, xor and not operator has been defined to correctly model unknown values. So this code is ok , or we need to remodel?

thanks.

 

[TrickyDicky]

Yes, they will correctly model unknown value by outputting unknown. any unknown in the equation will cause the output to be unknown (or 'X')

So yes, the code is ok - it defines a boolean equation.

But on real hardware, only '1' and '0' exist. Unknown is just a simulation concept.