Hey rajakash, Unsigned is internally treated like a number, and, of course, unsigned, range 0 to 255. std_logic_vector, is a vector, and you can assign, for example, a don´t care ('X') a tri-state ('Z'), and take one bit indepenently, for example, if you want the 4 bit, you can assign: test_vector <= test(4) --test_vector receives the 4th bit. any doubt, just ask!!!