[VHDL实例]最高优先级编码器

 -- Highest Priority Encoder
 -
 LIBRARY ieee;
 USE ieee.std_log_1164.ALL;
 entity priority is
    port(I : in bit_vector(7 downto 0); --inputs to be prioritised  
       A : out bit_vector(2 downto 0); --encoded output
       GS : out bit);  --group signal output
 end priority;
 
 architecture v1 of priority is
 begin
    process(I)
    begin
       GS <= '1'; --set default outputs
       A <= "000";
       if I(7) = '1' then
     A <= "111";
       elsif I(6) = '1' then
     A <= "110";
       elsif I(5) = '1' then
     A <= "101";
       elsif I(4) = '1' then
     A <= "100";
       elsif I(3) = '1' then
     A <= "011";
       elsif I(2) = '1' then
     A <= "010";
       elsif I(1) = '1' then
     A <= "001";
       elsif I(0) = '1' then
     A <= "000";
       else
     GS <= '0';
       end if;
    end process;   
 end v1;