light.vhd

软件开发环境：ISE 7.1i 仿真环境：ModelSim SE 6.0 1. 用VHDL语言仿真交通灯

----------红绿灯设计-------------
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
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entity light is
port(clk,rst:in std_logic;
	cout:out std_logic_vector(2 downto 0));
end;
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architecture one of light is
constant timered:integer:=9;
constant timegreen:integer:=9;
constant timeyellow:integer:=4;
type states is(red,green,yellow);
signal current_state,next_state:states;
signal time,delaytime:integer range 0 to 20;
signal temp:std_logic_vector(2 downto 0);
begin
----------时序逻辑电路-----------
REG:process(clk,rst)
	begin
	if rst='1' then current_state<=red;time<=0;
	elsif clk'event and clk='1' then
		if time=delaytime then current_state<=next_state;time<=0;
		else time<=time+1;
		end if;
	end if;
	end process REG;
----------组合逻辑电路-----------
COM:process(current_state)
	begin
	case current_state is
	when red=>temp<="100";next_state<=green;delaytime<=timegreen;
	when green=>temp<="010";next_state<=yellow;delaytime<=timeyellow;
	when yellow=>temp<="001";next_state<=red;delaytime<=timered;
	when others=>null;
	end case;
	cout<=temp;
	end process COM;
end;
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