ISRO 2011-ECE Computer Architecture

Question

Which of the following statement regarding a constant is not true

a. Constant defined in a package can be referenced by any entity or architecture for which package is used.

b. The value of constant can be changed with in the design description

c. Constant defined in an architecture is visible only to that architecture

d. Constant defined in a process declarative region is not visible outside that process

Answer 1

In VHDL (VHSIC Hardware Description Language), a constant is a value that cannot be changed once it is defined. This is the core property of a constant — it's immutable.

Let's analyze the options:

• a. Constant defined in a package can be referenced by any entity or architecture for which package is used
   True — Constants in packages are global to the design units that use the package.

• b. The value of constant can be changed within the design description
   Not True — Constants cannot be changed once defined. This statement is false.

• c. Constant defined in an architecture is visible only to that architecture
   True — Its scope is local to that architecture.

• d. Constant defined in a process declarative region is not visible outside that process
  True — Its scope is limited to the process block.