1、該售貨機的功能為每件商品25元，投入總金額大于25元時可找回零錢。（如圖為狀態(tài)轉移圖）
2、使用VHDL實現(xiàn)

library IEEE; use IEEE.STD_LOGIC_1164.ALL; entity veding_machine isport(clk,rst: in std_logic;nickel_in,dime_in,quarter_in : in std_logic;candy_out,nickel_out,dime_out:out std_logic); end veding_machine; ------------------------------------------------- architecture Behavioral of veding_machine istype state is (st0,st5,st10,st15,st20,st25,st30,st35,st40,st45);signal present_state,next_state : state; beginprocess (rst,clk)beginif(rst='1') then present_state <= st0;elsif(clk'event and clk ='1')thenpresent_state<= next_state;end if;end process; ------------------------------------- process(present_state,nickel_in,dime_in,quarter_in) begincase present_state iswhen st0 =>candy_out <= '0';nickel_out <='0';dime_out <='0';if (nickel_in= '1') then next_state <= st5;elsif(dime_in= '1') then next_state<= st10;elsif(quarter_in= '1') then next_state <= st25;else next_state <= st0;end if ;when st5 =>candy_out <= '0';nickel_out <='0';dime_out <='0';if (nickel_in= '1') then next_state <= st10;elsif(dime_in= '1') then next_state<= st15;elsif(quarter_in= '1') then next_state <= st30;else next_state <= st5;end if ;when st10 =>candy_out <= '0';nickel_out <='0';dime_out <='0';if (nickel_in= '1') then next_state <= st15;elsif(dime_in= '1') then next_state<= st20;elsif(quarter_in= '1') then next_state <= st35;else next_state <= st10;end if ;when st15 =>candy_out <= '0';nickel_out <='0';dime_out <='0';if (nickel_in= '1') then next_state <= st20;elsif(dime_in= '1') then next_state<= st25;elsif(quarter_in= '1') then next_state <= st40;else next_state <= st15;end if ;when st20 =>candy_out <= '0';nickel_out <='0';dime_out <='0';if (nickel_in = '1') then next_state <= st25;elsif(dime_in= '1') then next_state<= st30;elsif(quarter_in= '1') then next_state <= st35;else next_state <= st20;end if ;when st25 =>candy_out <= '1';nickel_out <='0';dime_out <='0';next_state <= st0;when st30 =>candy_out <= '1';nickel_out <='1';dime_out <='0';next_state <= st0;when st35 =>candy_out <= '1';nickel_out <='0';dime_out <='1';next_state <= st0;when st40 =>candy_out <= '0';nickel_out <='1';dime_out <='0';next_state <= st35;when st45 =>candy_out <= '0';nickel_out <='0';dime_out <='1';next_state <= st35;end case; end process; end Behavioral;

3、生成原理圖

4、添加testbench在modelsim中仿真

LIBRARY ieee; USE ieee.std_logic_1164.ALL;ENTITY tb_candy IS END tb_candy;ARCHITECTURE behavior OF tb_candy IS COMPONENT veding_machinePORT(clk : IN std_logic;rst : IN std_logic;nickel_in : IN std_logic;dime_in : IN std_logic;quarter_in : IN std_logic;candy_out : OUT std_logic;nickel_out : OUT std_logic;dime_out : OUT std_logic);END COMPONENT;--Inputssignal clk : std_logic := '0';signal rst : std_logic := '0';signal nickel_in : std_logic;signal dime_in : std_logic;signal quarter_in : std_logic;--Outputssignal candy_out : std_logic;signal nickel_out : std_logic;signal dime_out : std_logic;-- Clock period definitionsconstant clk_period : time := 10 ns;BEGINuut: veding_machine PORT MAP (clk => clk,rst => rst,nickel_in => nickel_in,dime_in => dime_in,quarter_in => quarter_in,candy_out => candy_out,nickel_out => nickel_out,dime_out => dime_out);clk_process :processbeginclk <= '0';wait for clk_period/2;clk <= '1';wait for clk_period/2;end process;stim_proc: processbegin rst <= '1';wait for 10 ns; rst <= '0';wait;end process;buy_candy: processbegin nickel_in <= '1';dime_in <= '0';quarter_in <= '0';wait for 40 ns;nickel_in <= '0';dime_in <= '1';quarter_in <= '0';wait for 40 ns;nickel_in <= '0';dime_in <= '0';quarter_in <= '1';wait;end process; END;

查看仿真波形：

總結

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