Using Component Declarations and Local Bindings

• Component declarations define interfaces for idealized local objects

  • Component declarations may be placed in architecture declarations or in package declarations

• Component instantiations connect local signals to component interface signals

USE work.resources.all;

ARCHITECTURE struct_2 OF reg4 IS

COMPONENT reg1 IS

PORT (d, clk : IN level;

q : OUT level);

END COMPONENT reg1;

CONSTANT enabled : level := '1';

FOR ALL : reg1 USE work.dff(behav)

PORT MAP(d=>d,clk=>clk,enable=>enabled,q=>q,qn=>OPEN);

BEGIN

r0 : reg1 PORT MAP (d=>d0,clk=>clk,q=>q0);

r1 : reg1 PORT MAP (d=>d1,clk=>clk,q=>q1);

r2 : reg1 PORT MAP (d=>d2,clk=>clk,q=>q2);

r3 : reg1 PORT MAP (d=>d3,clk=>clk,q=>q3);

END struct_2;

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This example shows the three steps listed earlier:

1) A component declaration defines the interface to an idealized local component. Note that the component declaration may be placed in a package declaration and made visible to the architecture via a USE clause.

2) A binding indication assigns a VHDL entity/architecture object to component instances. In this case, all reg1 components will use the behav architecture description for the dff entity in the work library.

3) Instantiation statements create copies of the component to be plugged into the architecture description by connecting local signals to signals in the component interface.