vhdl实现基于状态机的倒计时
时间: 2023-12-11 11:04:02 浏览: 25
以下是一个简单的基于状态机的倒计时 VHDL 代码示例:
```vhdl
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
entity Counter is
Port ( clk : in STD_LOGIC;
reset : in STD_LOGIC;
load : in STD_LOGIC;
count_done : out STD_LOGIC_VECTOR(3 downto 0);
count : out STD_LOGIC_VECTOR(7 downto 0));
end Counter;
architecture Behavioral of Counter is
type state_type is (idle, load_count, count_down);
signal state, next_state : state_type;
signal counter_reg : std_logic_vector(7 downto 0);
signal counter_next : std_logic_vector(7 downto 0);
begin
process (clk, reset)
begin
if reset = '1' then
state <= idle;
counter_reg <= (others => '0');
elsif rising_edge(clk) then
state <= next_state;
counter_reg <= counter_next;
end if;
end process;
process (state, load, counter_reg)
begin
case state is
when idle =>
if load = '1' then
next_state <= load_count;
else
next_state <= idle;
end if;
when load_count =>
next_state <= count_down;
counter_next <= counter_reg;
if load = '0' then
counter_next(7 downto 4) <= "0000";
counter_next(3 downto 0) <= count_done;
end if;
when count_down =>
next_state <= count_down;
counter_next <= counter_reg - 1;
if counter_reg = "00000001" then
next_state <= idle;
end if;
end case;
end process;
count <= counter_reg;
count_done <= counter_reg(3 downto 0);
end Behavioral;
```
该代码使用了以下三个状态:
1. 空闲状态(idle)
2. 装载计数值状态(load_count)
3. 倒计时状态(count_down)
当计数器处于空闲状态时,可以通过输入信号 `load` 装载计数器的初始值。当计数器处于装载计数值状态时,输入信号 `load` 被忽略,计数器的初始值被存储在 `counter_reg` 寄存器中。在此状态下,可以通过将计数器的低 4 位存储在输出信号 `count_done` 中来指示倒计时的结束。在倒计时状态下,计数器每次递减 1,直到计数器的值等于 1 时,计数器将返回到空闲状态。
请注意,此代码仅作为示例,并且可能需要进行修改以适应您的具体应用场景。