EEPW论坛

解（1）：条件赋值语句 
3到8译码器设计(条件赋值语句实现)
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;     
USE IEEE.STD_LOGIC_UNSIGNED.ALL; --为使用类型转换函数，打开此程序包。
ENTITY decoder3to8 IS       
  port(   DIN: IN  STD_LOGIC_VECTOR(2 DOWNTO 0);              
          DOUT: OUT BIT_VECTOR(7 DOWNTO 0));
END decoder3to8;     
ARCHITECTURE behave OF decoder3to8 IS    
BEGIN      
  WITH CONV_INTEGER(DIN) SELECT     
  DOUT<="00000001" WHEN 0,            
        "00000010" WHEN 1,            
        "00000100" WHEN 2,           
        "00001000" WHEN 3,            
        "00010000" WHEN 4,            
        "00100000" WHEN 5,            
        "01000000" WHEN 6,            
        "10000000" WHEN 7,             
        UNAFFECTED WHEN OTHERS;
END behave;

（2）：case语句
 3到8译码器设计(case语句实现)
 LIBRARY IEEE;     
 USE IEEE.STD_LOGIC_1164.ALL;     
 USE IEEE.STD_LOGIC_UNSIGNED.ALL; --为使用类型转换函数，打开此程序包。  ENTITY decoder3to8 IS
    port(   DIN: IN  STD_LOGIC_VECTOR(2 DOWNTO 0);   
           DOUT: OUT BIT_VECTOR(7 DOWNTO 0));
 END decoder3to8;
 ARCHITECTURE behave OF decoder3to8 IS    
 BEGIN      
   PROCESS (DIN)     
   BEGIN  
        CASE CONV_INTEGER(DIN) IS
           WHEN 0 => DOUT<="00000001";
           WHEN 1 => DOUT<="00000010";
           WHEN 2 => DOUT<="00000100";
           WHEN 3 => DOUT<="00001000";
           WHEN 4 => DOUT<="00010000";
           WHEN 5 => DOUT<="00100000";
           WHEN 6 => DOUT<="01000000";
           WHEN 7 => DOUT<="10000000";
           WHEN OTHERS => NULL;
        END CASE;
    END PROCESS;
 END behave
（3）：if_else语句
- 3到8译码器设计(if_else语句实现)
 LIBRARY IEEE;
 USE IEEE.STD_LOGIC_1164.ALL;   
 USE IEEE.STD_LOGIC_UNSIGNED.ALL; --为使用类型转换函数，打开此程序包。
 ENTITY decoder3to8 IS
   port(   DIN: IN  STD_LOGIC_VECTOR(2 DOWNTO 0);
            DOUT: OUT BIT_VECTOR(7 DOWNTO 0));  
 END decoder3to8;    
 ARCHITECTURE behave OF decoder3to8 IS
 BEGIN     
   PROCESS (DIN)    
   BEGIN    
   IF    CONV_INTEGER(DIN)=0 THEN DOUT<="00000001";
   ELSIF CONV_INTEGER(DIN)=1 THEN DOUT<="00000010";
   ELSIF CONV_INTEGER(DIN)=2 THEN DOUT<="00000100";
   ELSIF CONV_INTEGER(DIN)=3 THEN DOUT<="00001000";   
   ELSIF CONV_INTEGER(DIN)=4 THEN DOUT<="00010000";   
   ELSIF CONV_INTEGER(DIN)=5 THEN DOUT<="00100000";   
   ELSIF CONV_INTEGER(DIN)=6 THEN DOUT<="01000000";   
   ELSIF CONV_INTEGER(DIN)=7 THEN DOUT<="10000000";   
   END IF;     
   END PROCESS; 
 END behave;
（4）：移位操作符 
 3到8译码器设计(移位操作实现)
 LIBRARY IEEE;     
 USE IEEE.STD_LOGIC_1164.ALL;     
 USE IEEE.STD_LOGIC_UNSIGNED.ALL; --为使用类型转换函数，打开此程序包。  ENTITY decoder3to8 IS     
   port(   DIN: IN  STD_LOGIC_VECTOR(2 DOWNTO 0);    
            DOUT: OUT BIT_VECTOR(7 DOWNTO 0)); 
 END decoder3to8;
 ARCHITECTURE behave OF decoder3to8 IS  
 BEGIN    
   DOUT<="00000001" SLL CONV_INTEGER(DIN); --被移位部分是常数 
 END behave;

3.14
LIBRARY  IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
 ENTITY vote_7 IS
PORT( DIN:  IN STD_LOGIC_VECTOR(6 DOWNTO 0);--7位表决输入(1:同意，0:不同意)
G_4: OUT STD_LOGIC;           --超过半数指示
CNTH: OUT STD_LOGIC_VECTOR(2 DOWNTO 0));--表决结果统计数
END vote_7;
ARCHITECTURE BHV OF vote_7 IS
BEGIN
PROCESS(DIN)
VARIABLE Q: STD_LOGIC_VECTOR(2 DOWNTO 0);
BEGIN
Q:="000";
FOR n IN 0 TO 6 LOOP   --n是LOOP的循环变量
IF(DIN(n)='1') THEN Q:=Q+1; END IF;
 END LOOP;
 CNTH<=Q;
IF Q>=4 THEN G_4<='1'; ELSE G_4<='0'; END IF;
 END PROCESS;
END BHV;