Concurrent Signal Assignments :

Concurrent signal assignment is process for sequential assignment. The concurrent signal assignment statements are to be indicated into architecture. Concurrent signal assignment is independent of statements inside architecture and executed concurrently. For multiple assignments multiple drivers are created. Concurrent signal assignment types are, 1) Simple Concurrent Signal Assignments , 2) Conditional Concurrent Signal Assignment, 3) Selected Concurrent Signal Assignments and 4) Guarded Concurrent Signal Assignments Simple Signal Assignments : The syntax is : Name_of_signal <= expression;

Example 1 :

block
	signal A, B, Z: BIT;
	begin
	Z <= A and B;
	end block;

Example 2 :

entity simpsig is
		port	(a, b, e: in std_logic;
			c, d: out std_logic);
	end simpsig;
	architecture xpld of simpsig is
	begin
	c <= a and b;			--	creates an AND gate
	d <= e;               		--	connects two nodes
	end xpld;	

Example 3 :

library  ieee ;
	use ieee.std_logic_1164.all ;
	use ieee.std_logic_signed.all ;
	entity adder  is
		port	(Cin : in std_logic ;
			X, Y: in std_logic_vector (3 downto 0) ;
			S: out std_logic_vector (3 downto 0) ;
			Cout: out std_logic) ;
	end adder ;
        architecture behave_arch of adder is
	signal Sum: std_logic_vector (4 downto 0) ;
	begin
		Sum <= ('0' & X) + Y + Cin ;
		S <= Sum (3 downto 0);
		Cout <= Sum (4) ;
end behave_arch ;