traffic.vhd

简单的交通灯,功能为红灯,黄灯,绿灯轮流亮,时间多少可以改变

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use ieee.std_logic_arith.all;
entity traffic is
port(clk : in std_logic;
       ql : out std_logic_vector(7 downto 0);
       qh : out std_logic_vector(7 downto 0);
     red : out std_logic := '0';
     green : out std_logic := '1';
     yellow : out std_logic );
end traffic;
architecture lights of traffic is
signal timeh : std_logic_vector(3 downto 0) := "0101" ;
signal timel : std_logic_vector(3 downto 0) := "1010" ;
signal exc : bit := '1' ;
begin
   process (clk,timeh,timel,exc)
   begin
    if(timeh = "0000" and timel < "0011") then
	      yellow <= '1' ;
	      red <= '0' ;
	      green <= '0' ; 
	      ql <= "00000000" ;
	      qh <= "00000000" ;
	      	  else if(exc = '0') then
	          red <= '1';
	          yellow <= '0';
	       else
	          green <= '1' ;
		  yellow <= '0' ;
	       end if; 
	       
	       case timel is
	       
	       when "0000" => ql <= "00111111";
	       when "0001" => ql <= "00000110";
	       when "0010" => ql <= "01011011";
	       when "0011" => ql <= "01001111";
	       when "0100" => ql <= "01100110";
	       when "0101" => ql <= "01101101";
	       when "0110" => ql <= "01111101";
	       when "0111" => ql <= "00000111";
	       when "1000" => ql <= "01111111";
	       when "1001" => ql <= "01101111";
	       when others => ql <= "00000000";
	       end case;
          
	       case timeh is
	    
	       when "0000" => qh <= "00111111";
	       when "0001" => qh <= "00000110";
	       when "0010" => qh <= "01011011";
	       when "0011" => qh <= "01001111";
	       when "0100" => qh <= "01100110";
	       when "0101" => qh <= "01101101";
	       when others => qh <= "00000000";
	       end case;
	  
	  end if;    
   if(clk 'event and clk='1') then
        if(timel = "0000") then
	      timel <= "1001";
	      if(timeh = "0000") then
	         timeh <= "0101";
	         exc <= NOT exc;
	      else
	         timeh <= timeh - '1' ;
	      end if;
	  else 
	     timel <= timel - '1' ;
	  end if;
    
	 
      end if;
   end process;
end lights;