Several previous study note show that the conditional and selected signal assignment statements can be rewritted by the simple if and case statements.

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large <= a when a > b else b;
small <= b when a > b else a;

Since there are two comparators in code. However, the same function can be coded by a single if statement:

if a> b then
large <= a;
small <= b;
large <= b;
small <= a;
end if;

Only one relational operator in code.

Although a process is flexible, a unitended memory problem may be occured(The VHDL standard specifies that a signal will kepp its previous value if it is not assigned in a process).
It’s better to follow these rules below while developing code for a combinational cirucit:

  1. include all input signals in the sensitivity list.
  2. include the else branch in an if statement.
  3. assign a value to every signal in every branch.
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Dr. Lu


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