Hi I have 2 component instatiation inst1 : test_component port map ( b_in => in_sig, a_out => sig_x(7 downto 0) ); inst2 : component2 port map ( c => sig_x(3 downto 0)&sig_x(7 downto 4), d => out_sig ); for testing purpose, i have to swap the vectors in inst2 ( c => sig_x(3 downto 0)&sig_x(7 downto 4)) i tried this .. sigc<=sig_x(3 downto 0)&sig_x(7 downto 4); inst2 : component2 port map ( c => sigc, d => out_sig ); it still does not work ...i read that expressions can be used in instantiation when the operands are contants ...is there any other way to solve this?