The instantiation of entity objects is similar to the instantiation of normal entities. There are two possibilities: direct and indirect instantiation.
The indirect instantiation first declares and instantiates a component which can be seen as something like a virtual instance. This virtual instance becomes a real one by binding the component to an entity/architecture pair. The binding can be done explicitly in a configuration or implicitly by default rules.
The example on the right illustrates this binding. In the configuration CONF the component E is bound to the entity/architecture pair E(A) from Chapter 6.1.4. This explicit binding can be omitted because the component also would be bound to the entity E by default rules because their names and effective interface lists are identical.
Note: Inherited concurrent component instantiations have to be configured again, also if this was already done for the parent architecture because configurations are not inherited.
entity E_Struct is
port(A: in Bit; B: out Bit);
end E_Struct;
architecture Structure of E_Struct is
component E
port(Clk: in Bit; Output: out Bit);
end component;
begin
I1: E
port map(Clk => A; Output => B);
end Structure;
configuration CONF of E_Struct is
for Structure
for all: E use entity Work.E(A)
port map(Clk => Clk; Output => Output);
end for;
end for;
end CONF;