vhdl 简易交通灯的设计代码

以下是一个简单的交通信号灯的VHDL代码示例：

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity traffic_light is
    port (
        clk : in std_logic;
        reset : in std_logic;
        red : out std_logic;
        yellow : out std_logic;
        green : out std_logic
    );
end traffic_light;

architecture Behavioral of traffic_light is
    type state_type is (stop, ready, go, caution);
    signal current_state, next_state : state_type;

    -- 定义常量
    constant red_time : integer := 20;
    constant yellow_time : integer := 2;
    constant green_time : integer := 20;

begin
    -- 状态转移逻辑
    process (clk, reset)
    begin
        if reset = '1' then
            current_state <= stop;
        elsif rising_edge(clk) then
            current_state <= next_state;
        end if;
    end process;

    -- 状态转移输出逻辑
    process (current_state)
    begin
        case current_state is
            when stop =>
                red <= '1';
                yellow <= '0';
                green <= '0';
                next_state <= ready after red_time * 1000000;
            when ready =>
                red <= '1';
                yellow <= '1';
                green <= '0';
                next_state <= go after yellow_time * 1000000;
            when go =>
                red <= '0';
                yellow <= '0';
                green <= '1';
                next_state <= caution after green_time * 1000000;
            when caution =>
                red <= '0';
                yellow <= '1';
                green <= '0';
                next_state <= stop after yellow_time * 1000000;
            when others =>
                red <= '0';
                yellow <= '0';
                green <= '0';
                next_state <= stop;
        end case;
    end process;

end Behavioral;

该代码定义了一个名为`traffic_light`的实体，该实体具有时钟(`clk`)和复位(`reset`)输入，以及红、黄和绿三个输出。在实体的体系结构中，使用了状态机来实现状态转移和输出逻辑。在每个状态下，代码设置输出信号的值，同时计算下一个状态的值，并在指定的时间后完成状态转移。

注意，这只是一个简单的代码示例，仅用于参考和学习。在实际的设计中，需要更加详细和精确地定义状态机，并根据实际需求进行调整和优化。