====== Constant declarations ======
===== constant_declaration =====
<code vhdl>
constant identifier_list : subtype_indication [ := expression ] ;
</code>

===== Parents =====
  * entity_declarative_part
  * architecture_declarative_part
  * package
  * package_body
  * block_declarative_part
  * function_declarative_part
  * procedure_declarative_part
  * process_declarative_part

===== Further definitions =====
==== identifier_list ====
''[[.:bnf#identifier]] {, [[.:bnf#identifier]] }''

==== subtype_indication ====
''[ resolution_function_ [[.:bnf#name]] ] [[.:bnf#type_mark]] [ [[.:bnf#constraint]] ]''

==== expression ====
  * [[.:bnf#relation]] { and relation }
  * relation { or relation }
  * relation { xor relation }
  * relation [ nand relation ]
  * relation [ nor relation ]
  * relation { xnor relation }

===== Examples =====
The constant //cte// is of the type integer and has the value 5. The constants //Vdd// and //Vcc// are of the type //bit// and have the value '1'. The constant //minimum_setup-_time// is of the physical type //time// and has the value 5 ns.
<code vhdl>
CONSTANT cte : integer := 5 ;
CONSTANT Vdd, Vcc : bit := '1' ;
CONSTANT minimum_setup_time :
      time := 5 ns ;
</code>

----

  * The constant //name// contains the string " //Dupond// ".
  * The bit vector //address// has the constant value "00110110".
  * The constant //mask// is declared as a subtype of //bit_vector// with the value "0101".
  * The constant //bittab// is declared as a subtype of //bit_vector// with the value "000111Z1Z".
  * The constant //tab// is declared as a subtype of //table_type// with the individual elements being assigned the constant values 2, 3, 4, -2 and 0.

<code vhdl>
CONSTANT name : string := "Dupond" ;

CONSTANT address : bit_vector := "00110110" ;

CONSTANT mask : bit_vector( 1 TO 3 ) := "0101" ;

CONSTANT bittab : bit_vector( 1 TO 9 ) :=
      ( 1 TO 3 => '0', 7 | 9 => 'Z', OTHERS => '1' ) ;

CONSTANT tab : table_type( 0 TO 4 ) :=
      ( 2, 3, 4, -2, 0 ) ;
</code>

----

An incomplete declaration of a constant, such as that of //deferred// shown here, may only be contained in the package declaration. The complete declaration of the constant has to be contained in the package body. If the constant`s value is changed only the //PACKAGE BODY// has to be newly translated and none of the design units which are constructed upon the package are affected.
<code vhdl>
PACKAGE P IS
   CONSTANT deferred : integer ;
END P;

PACKAGE BODY P IS
   CONSTANT deferred : integer := 200 ;
END P ;
</code>