-- Copyright © 1993 by  McGraw-Hill, Inc. and Zainalabedin Navabi

-- FIGURE 4.24 




-- ENTITIY DECLERATION OF NIBBLE COMPARATOR FOR TEST BENCH :
ENTITY nibble_comparator_test_bench IS
END nibble_comparator_test_bench ;
--



--  TEST BENCH FOR ITERATIVE ARCHITECTURE OF NIBBLE COMPARATOR :

ARCHITECTURE input_output OF nibble_comparator_test_bench IS
  COMPONENT comp4 PORT (a, b : IN bit_vector (3 DOWNTO 0);
                        a_gt_b, a_eq_b, a_lt_b : IN BIT;
                        a_gt_b_out, a_eq_b_out, a_lt_b_out : OUT BIT);
  END COMPONENT;
  FOR a1 : comp4 USE ENTITY WORK.nibble_comparator(iterative);
  SIGNAL a, b : BIT_VECTOR (3 DOWNTO 0); 
  SIGNAL eql, lss, gtr : BIT;
  SIGNAL vdd : BIT := '1';
  SIGNAL gnd : BIT := '0';
BEGIN
  a1: comp4 PORT MAP (a, b, gnd, vdd, gnd, gtr, eql, lss);
  a2:  a <= "0000",          ---- a = b (steady state)
         "1111" AFTER 0500 NS, -- a > b (worst case)
         "1110" AFTER 1500 NS, -- a < b (worst case)
         "1110" AFTER 2500 NS, -- a > b (need bit 1 info)
         "1010" AFTER 3500 NS, -- a < b (need bit 2 info)
         "0000" AFTER 4000 NS, -- a < b (steady state, prepare for next)
         "1111" AFTER 4500 NS, -- a = b (worst case)
         "0000" AFTER 5000 NS, -- a < b (need bit 3 only, best case)
         "0000" AFTER 5500 NS, -- a = b (worst case)
         "1111" AFTER 6000 NS; -- a > b (need bit 3 only, best case)
  a3 : b <= "0000",          ---- a = b (steady state)
         "1110" AFTER 0500 NS, -- a > b (worst case)
         "1111" AFTER 1500 NS, -- a < b (worst case)
         "1100" AFTER 2500 NS, -- a > b (need bit 1 info)
         "1100" AFTER 3500 NS, -- a < b (need bit 2 info)
         "1111" AFTER 4000 NS, -- a < b (steady state, prepare for next)
         "1111" AFTER 4500 NS, -- a = b (worst case)
         "1111" AFTER 5000 NS, -- a < b (need bit 3 only, best case)
         "0000" AFTER 5500 NS, -- a = b (worst case)
         "0000" AFTER 6000 NS; -- a > b (need bit 3 only, best case)
END input_output;