Generics:

Generics are mainly similar to constants whose values supplied externally. Similar to ports, generics are declared in entities and component declarations. The important advantage of generic is it provide a data transfer. The values of generics declared in an entity. The Syntax is :

generic ( generic_interface_list ) ;

Example :

library ieee ;
	use ieee.std_logic_1164.all;
           package components is
	     component system
	           generic ( n : integer := 4 ) ;
	                port ( cin: in std_logic ;
	                          x, y: in std_logic_vector(n-1 downto 0) ;
	                          s: out std_logic_vector(n-1 downto 0) ;
	                          cout: out std_logic ) ;
	    end component ;
	    component SR
	           generic ( n : integer := 4 ) ;
	                port ( d: in std_logic_vector(n-1 downto 0) ;
	                          resetn: in std_logic ;
	                          e, clock: in std_logic ;
	                         q: out std_logic_vector(n-1 downto 0) ) ;
	end component;