Perhaps you mean a top architecture with 12 instances of some entity.
Each instance has a unique label:
my_entity_1 : entity work.my_entity port map (reset => reset_sig, -- [in] clk => clk_sig, -- [in] i => i_1_sig, -- [in] o => o_1_sig); -- [out]
my_entity_12 : entity work.my_entity port map (reset => reset_sig, -- [in] clk => clk_sig, -- [in] i => i_12_sig, -- [in] o => o_12_sig); -- [out]
The signal associated with an instance port is whatever you define it to be in the port map. I think of this as "wiring up" the instances. These "wire" signals must be declared between the IS and BEGIN of the top architecture. It can be a different signal for each instance if you like.
These signals are accessible anywhere in the top architecture.
-- Mike Treseler