8-3优先编码器(when-else实现)和（if-elsif-else实现）

（一）8-3优先编码器(when-else实现)：

LIBRARY IEEE;

USE IEEE.STD_LOGIC_1164.ALL;

 

ENTITY coder IS

PORE(

                 D:IN STD_LOGIC_VECTOR(7 DOWNTO 0);

          output:OUT STD_LOGIC_VECTOR(2 DOWNTO 0)

          );

END coder;

 

ARCHITECTURE art1 IS

BEGIN

   output<="000" WHEN D(7)='0' ELSE

                 "001" WHEN D(6)='0' ELSE

                 "010" WHEN D(5)='0' ELSE

                 "011" WHEN D(4)='0' ELSE

                 "100" WHEN D(3)='0' ELSE

                 "101" WHEN D(2)='0' ELSE

                 "110" WHEN D(1)='0' ELSE

                 "111";

END art1;

（二）8-3优先编码器（if-elsif-else实现）：

 

LIBRARY IEEE;

USE IEEE.STD_LOGIC_1164.ALL;

 

ENTITY coder IS

PORT(

                  D:IN STD_LOGIC_VECTOR(7 DOWNTO 0);

           output:OUT STD_LOGIC_VECTOR(2 DOWNTO 0)

          );

END coder;

 

ARCHITECTURE art1 OF coder IS

BEGIN

       PROCESS(D)

       BEGIN

            IF        D(7)='0' THEN output<="000";

            ELSIF D(6)='0' THEN output<="001";

            ELSIF D(5)='0' THEN output<="010";

            ELSIF D(4)='0' THEN output<="011";

            ELSIF D(3)='0' THEN output<="100";

            ELSIF D(2)='0' THEN output<="101";

            ELSIE D(1)='0' THEN output<="110";

            ELSE                         output<="111";

            END IF;

     END PROCESS;

END art1;