decoder3_8.vhd

出租车计费器,VHDL实现

library ieee;
use  ieee.std_logic_1164.all;
use  ieee.std_logic_unsigned.all;
entity decoder3_8 is
port(
     quiclk:in  std_logic;
     wei8:out std_logic_vector(7 downto 0)
    );
end decoder3_8;
architecture func of decoder3_8 is
signal  choice :std_logic_vector(2 downto 0);
begin
  process(quiclk)
      begin
        if(quiclk'event and quiclk='1') then
          if(choice="111") then
             choice<="000";
          else
              choice<=choice+1;
          end if;
        end if; 
    end process;

with choice select
    wei8<="10000000" when "000",
          "01000000" when "001",
          "00100000" when "010",
          "00010000" when "011",
          "00001000" when "100",
          "00000100" when "101",
          "00000010" when "110",
          "00000001" when "111",
          "00000000" when others;
end func;