nclight.txt

利用硬件描述语言VHDL设计交通灯电路,设计一个十字路口交通灯控制器

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
USE ieee.std_logic_unsigned.ALL;

ENTITY nclight IS
Port(clk : in  std_logic;
 ra,rb,ya,yb,ga,gb : out std_logic );
END nclight;

Architecture a of nclight is
type state is (S0,S1,S2,S3);
signal presentstate,nextstate  : state;
signal tmp1,tmp2 : integer range 0 to 40;
signal timeout1,timeout2: std_logic;
signal q: std_logic_vector(21 downto 0);
signal sec: std_logic;
Begin
----get 1 hz clock pulse
process(clk)
begin
if clk'event and clk='1' then    q<=q+1; end if;
sec<=q(21);  --get 1 hz clock pulse
end process;
timing: process(sec)
begin
if sec'event and sec='1' then
 if tmp1=39 then  timeout1<='1';   timeout2<='0';  tmp1<=0;  else
   if timeout1='1' then 
     if tmp2=4 then  timeout2<='1';   timeout1<='0';   tmp2<=0;
        else   tmp2<=tmp2+1;    end if; 
     else    tmp1<=tmp1+1;    end if; 
 end if; 
 end if;
end process;
changestate: process(presentstate)
Begin    
case presentstate is
        when S0 => if timeout1='0' then 
                        nextstate<=s0; 
                        ra<='0'; ya<='0'; ga<='1'; 
                        rb<='1'; yb<='0'; gb<='0'; 
                else  nextstate<=s1;   end if;
        when S1 => if timeout2='0' then 
                       nextstate<=s1;
                      ra<='0'; ya<='1'; ga<='0'; 
                      rb<='1'; yb<='0'; gb<='0'; 
                    else  nextstate<=s2;  end if;        
when S2 => if timeout1='0' then 
                      nextstate<=s2; 
                      ra<='1'; ya<='0'; ga<=‘1'; 
                      rb<='0'; yb<='0'; gb<='1'; 
                    else nextstate<=s3; end if;
        when S3 => if timeout2='0' then 
                     nextstate<=s3;  
                     ra<='1'; ya<='0'; ga<='0'; 
                     rb<='0'; yb<='1'; gb<='0'; 
                    else  nextstate<=s0; end if;
        when others => nextstate<=s0;
                    timeout1<='0';     timeout2<='0';  
               end case;
end process;
end a;