Need help with understanding basic VHDL code for 4-to-2 priority encoder

[bobby19]

hey, Im looking for some help in the attached question. We have used VHDL a bit in the lab, but code was pretty much given to us...we have not been formally taught it.

I understand how the input and output vectors are declared and can be thought of as arrays, but I do not understand how this question can be answered. Can somebody please guide me through it.

Thanks a lot!

 

[tshankar501]

Re: Some Basic VHDL Help

In the code, the operation is defined only in the architecture and the one in the entity are like pins in a chip....

so in the architecture, we see that it is defined as follows.....The Most significant bit in y is y(0) and the MSB in w is w(0)....

so w(3) is the last bit on the right...so....from the first sentence inside the process, we infer that....

if w = XXX1 where X is the dont care, then y(0) =1;
if w = XX10, then y(0) = 0;
if w= X100, then y(0) = 1;
if w= X000, then y(0) = 0;


so, from now on....its basic digital....you can see that the answer is the third choice....by substituting each choice one by one, you could easily find it out.....