Well often in VHDL I notice that a certain component has multiple output ports. Ie in one of our examples we were given the following component:
COMPONENT eight_bitadder
PORT ( a, b: in std_logic_vector(7 downto 0);
f: in std_logic;
C: out std_logic_vector(7 downto 0);
o, z: out std_logic);
END COMPONENT;
Where z determines if the result is 0, and o triggers on overflow.
Now in my case I wish to use this adder, however the actual result is not of importance, rather I only wish to check if the result is "0". I could of course add a dummy signal and store the port to this signal, however that seems needlessly complicated, and might add extra components during synthesis?
When you instantiate the component you can leave the output ports that you don't care about open. The only signal you care about below is "overflow".
EDIT: Note that the synthesis tools will optimize away any outputs that are not being used.
EIGHT_BITADDER_INST : eight_bitadder
port map (
a => a,
b => b,
f => f,
c => open,
o => overflow,
z => open
);