sel2.vhd

出租车计价器

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity sel2 is
   port (clk:in std_logic;
         in1,in2,in3,in4:in std_logic_vector(3 downto 0);
         sel2:out std_logic_vector(0 downto 3);
         daout:out std_logic_vector(3 downto 0));    
end sel2;
architecture sel_arc of sel2 is
 begin
 PROCESS (clk)
   VARIABLE cnt:std_logic_vector(3 downto 0);
  BEGIN
  IF(clk'event AND CLK='1')THEN
            if cnt="0000"then
               cnt:="0001";
            elsif cnt="0001"then
                  cnt:="0010";
                elsif cnt="0010"then
                      cnt:="0100";
                    elsif cnt="0100"then
                           cnt:="1000";
            end if;
       case cnt is
    when"0001"=>daout<=in1;
    when"0010"=>daout<=in2;
    when"0100"=>daout<=in3;
    when"1000"=>daout<=in4;
    when others=>daout<="0000";
    end case;
   end if;
  sel2<=cnt;
  end process;
end sel_arc;