1.用vhdl实现三位全加器

用vhdl实现三位全加器

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       library ieee;

       use ieee.std_logic_.all;

       use ieee.std_logic_unsigned.all;

       use ieee.std_logic_arith.all;

       entity bit1adder is

        port(

        a,源码bytetcc源码分析b,ci:in std_logic;

        s,co:out std_logic

        );

       end bit1adder;

       architecture func of bit1adder is --此功能可由真值表推出，或者亦可直接列出真值表代替此程序

       signal:x,y:std_logic;

       begin

        x<=a xor b;

        y<=x and ci;

        s<=x xor ci;

        co<=y or (a and b);

       end func;

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       äºŒä½å…¨åŠ å™¨æºä»£ç å¦‚下：

       library ieee;

       use ieee.std_logic_.all;

       use ieee.std_logic_unsigned.all;

       use ieee.std_logic_arith.all; --此包含有类型转换函数

       entity bit2adder is

        port(

        a,b:in std_logic_vector(1 downto 0);

        ci:in std_logic;

        co:out std_logic;

        s:out std_logic_vector(1 downto 0)

        );

       end bit2adder;

       architecture func of bit2adder is

       begin

        process(a,b,ci) --更多位的也可按照此思路来写

        variable temp:std_logic_vector(2 downto 0);

        variable x,y,sum:ingeter;

        begin

        x:=conv_integer(a);

        y:=conv_integer(b);

        sum:=(x+y)+conv_integer(ci);

        temp:=conv_std_logic_vector(sum,3);

        s<=temp(1 downto 0);

        co<=temp(2);

        end process;

       end func;