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when s1 => dout <= \ when s2 => dout <= \ when s3 => dout <= \ end case; end process; end;
begin
if reset = '1' then state <= s0;
elsif rising_edge ( clock ) then case state is
when s0 => if din = '1' then state <= s1;
二进程mealy状态机
library ieee;
use ieee.std_logic_1164.all;
entity mealy_1 is port ( reset : in std_logic; clock : in std_logic; din : in std_logic;
dout : out std_logic_vector ( 2 downto 0 ) ); end entity;
architecture statemachine of mealy_1 is type state_type is ( s0, s1, s2, s3 ); signal state : state_type; begin
process ( reset, clock ) -- 变换状态
end if; when s1 => if din = '1' then state <= s2; end if; when s2 => if din = '1' then state <= s3; end if; when s3 => if din = '1' then state <= s0; else
state <= s1; end if; end case; end if; end process;
process ( state, din ) -- 输出
16
VHDL语法格式
begin
case state is
when s0 => if din='0' then dout <=\ else
dout <=\ end if; when s1 => if din='0' then dout <=\ else
dout <=\ end if; when s2 => if din='0' then dout <=\ else
dout <=\ end if; when s3 => if din='0' then dout <=\ else
dout <=\ end if; end case;
end process; end architecture;
三进程mealy状态机
library ieee;
use ieee.std_logic_1164.all;
entity mealy_2 is
port ( reset : in std_logic; clock : in std_logic; din : in std_logic;
dout : out std_logic_vector( 2 downto 0 ) ); end entity;
architecture statemachine of mealy_2 is type state_type is ( s0, s1, s2, s3 ); signal presentstate : state_type; signal nextstate : state_type; begin
process ( reset, clock ) -- 更新当前状态 begin
if reset = '1' then presentstate <= s0;
17
VHDL语法格式
elsif rising_edge ( clock ) then presentstate <= nextstate; end if; end process;
process ( presentstate, din ) -- 生成次态 begin
case presentstate is when s0 => if din ='1' then nextstate <= s1; else
nextstate <= s0; end if; when s1 => if din ='1' then nextstate <= s2; else
nextstate <= s1; end if; when s2 => if din ='1' then nextstate <= s3; else
nextstate <= s2; end if;
when s3 => if din = '1' then nextstate <= s0; else
nextstate <= s1; end if; end case; end process;
process ( presentstate, din ) -- 输出 begin
case presentstate is
when s0 => if din = '0' then dout <= \ else
dout <= \ end if;
when s1 => if din = '0' then dout <= \ else
dout <= \ end if;
when s2 => if din = '0' then dout <= \ else
18
VHDL语法格式
dout <= \ end if;
when s3 => if din = '0' then dout <= \ else
dout <= \ end if; end case; end process; end;
entity traffic_light is
port ( sensor : in std_logic; clock : in std_logic; red_light : out std_logic; green_light : out std_logic; yellow_light : out std_logic ); end traffic_light;
architecture simple of traffic_light is
type t_state is ( red, green, yellow ); -- 定义枚举状态
用状态机设计交通灯之一
-- -- -- -- -- -- -- 3 --
个进程的状态机。
这是一个简单的状态机设计实例，根据时钟变换路口 的红，绿，黄三个信号灯，从程序中可以看出，时钟 的周期至少应为，例如30秒。
这个状态机程序的程序的特点是，有2个进程，一个 进程负责生成次级状态和输出当前状态的输出信号， 一个进程负责更新当前状态。
除了本例中的2个进程的状态机外，还有1个进程与
signal present_state : t_state; -- 中间信号 signal next_state : t_state; begin
-- 以下过程生成次级状态并根据状态变换信号灯 process ( present_state, sensor) begin
case present_state is
when green => red_light <= '0'; green_light <= '1'; yellow_light <= '0'; next_state <= yellow; when red => red_light <= '1';
19
library ieee;
use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all;
VHDL语法格式
green_light <= '0'; yellow_light <= '0'; if sensor = '1' then
next_state <= green; -- 无人 else
next_state <= red; -- 有人 end if;
when yellow => red_light <= '0'; green_light <= '0'; yellow_light <= '1'; next_state <= red; end case; end process;
-- 以下过程更新当前状态
process begin
wait until clock'event and clock = '1'; present_state <= next_state; end process; end simple;
entity lighta is
port ( clock,din : in bit; dout : out bit ); end lighta;
architecture behaviour of lighta is type state_type is ( s0, s1, s2, s3 ); signal present_state : state_type; signal next_state : state_type; begin fb_logic:
process ( present_state, din ) -- 变换下一个状态并输出 begin
case present_state is when s0 => if din = '0' then dout <= '0'; next_state <= s0; else
dout <= '1';
用状态机设计交通灯之二
-- mealy type state machine example
next_state <= s2; end if;
20
VHDL语法格式