11.txt

用1位半减器构成一位全减器

用1位半减器构成一位全减器，之后再构成8位全减器。有三个组件：h_suber，一位半减器，f_suber，一位全减器，f_suber8，8位全减器。


另附VHDL代码：
--h_suber
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
ENTITY h_suber IS
PORT(x,y: IN STD_LOGIC;
diff,s_out:OUT STD_LOGIC);
END h_suber;
ARCHITECTURE behav OF h_suber IS
BEGIN
diff<=x XOR y;
s_out<=(NOT x) AND y;
END behav;
--end h_suber
--f_suber
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
ENTITY f_suber is
PORT(fx,fy,sub_in:IN STD_LOGIC;
diffr,sub_out:OUT STD_LOGIC);
END ENTITY f_suber;
ARCHITECTURE behav OF f_suber IS
COMPONENT h_suber
PORT(x,y : IN STD_LOGIC;
diff,s_out:OUT STD_LOGIC);
END COMPONENT;
SIGNAL a,b,c : STD_LOGIC;
BEGIN
u1:h_suber PORT MAP(x=>fx,y=>fy,diff=>a,s_out=>b);
u2:h_suber PORT MAP(x=>a,y=>sub_in,diff=>diffr,s_out=>c);
sub_out<=b OR c;
END behav;
--end f_suber
--f_suber8
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
ENTITY f_suber8 IS
PORT(fx8,fy8 :IN STD_LOGIC_VECTOR(7 DOWNTO 0);
sub_in8: IN STD_LOGIC;
diff8: OUT STD_LOGIC_VECTOR(7 DOWNTO 0);
s_out8: OUT STD_LOGIC);
END ENTITY f_suber8;
ARCHITECTURE behav OF f_suber8 IS
COMPONENT f_suber
PORT(fx,fy,sub_in:IN STD_LOGIC;
diffr,sub_out:OUT STD_LOGIC);
END COMPONENT;
SIGNAL s_outs: STD_LOGIC_VECTOR(6 DOWNTO 0);
BEGIN
u1 : f_suber PORT MAP(fx=>fx8(0),fy=>fy8(0),sub_in=>sub_in8,diffr=>diff8(0),sub_out=>s_outs(0));
u2 : f_suber PORT MAP(fx=>fx8(1),fy=>fy8(1),sub_in=>s_outs(0),diffr=>diff8(1),sub_out=>s_outs(1));
u3 : f_suber PORT MAP(fx=>fx8(2),fy=>fy8(2),sub_in=>s_outs(1),diffr=>diff8(2),sub_out=>s_outs(2));
u4 : f_suber PORT MAP(fx=>fx8(3),fy=>fy8(3),sub_in=>s_outs(2),diffr=>diff8(3),sub_out=>s_outs(3));
u5 : f_suber PORT MAP(fx=>fx8(4),fy=>fy8(4),sub_in=>s_outs(3),diffr=>diff8(4),sub_out=>s_outs(4));
u6 : f_suber PORT MAP(fx=>fx8(5),fy=>fy8(5),sub_in=>s_outs(4),diffr=>diff8(5),sub_out=>s_outs(5));
u7 : f_suber PORT MAP(fx=>fx8(6),fy=>fy8(6),sub_in=>s_outs(5),diffr=>diff8(6),sub_out=>s_outs(6));
u8 : f_suber PORT MAP(fx=>fx8(7),fy=>fy8(7),sub_in=>s_outs(6),diffr=>diff8(7),sub_out=>s_out8);
END behav;
--end f_suber8