基于VHDL +FPGA 的自动售货机控制模块的设计与实现
根据图1所示的状态转换图,用VHDL中的CASE_WHEN结构和IF_THEN_ELSE语句实现控制功能,源程序如下:
LIBRARY IEEE; --库和程序包的使用说明
USE IEEE.STD_LOGIC_1164.ALL;
ENTITY sellmachine IS --实体定义
PORT(clk,reset: IN std_logic;
state_inputs:IN std_logic_vector(0 TO 1);
comb_outputs:OUT std_logic_vector(0 TO 1));
END sellmachine;
ARCHITECTURE state OF sellmachine IS --结构体
TYPE fsm_st IS (S0,S1,S2,S3,S4); --状态枚举类型定义
SIGNAL current_state,next_state:fsm_st; --状态信号的定义
BEGIN
reg:PROCESS(reset,clk) --时序进程
BEGIN
IF reset='1' THEN current_state=S0; --异步复位
ELSIF rising_edge(clk) THEN
current_state=next_state; --状态转换
END IF;
END PROCESS;
corn:PROCESS(current_state,state_inputs) --组合进程
BEGIN
CASE current_state IS
WHEN S0=>comb_outputs=00; --现态S0
IF state_inputs=00 THEN next_state=S0; --输入不同,次态不同
ELSIF state_inputs=01 THEN next_state=S1;
ELSIF state_inputs=10 THEN next_state=S2;
END IF;
WHEN S1=>comb_outputs=00; --现态S1
IF state_inputs=00 THEN next_state=S1; --输入不同,次态不同
ELSIF state_inputs=01 THEN next_state=S2;
ELSIF state_inputs=10 THEN next_state=S3;
END IF;
WHEN S2=>comb_outputs=00; --现态S2
IF state_inputs=00 THEN next_state=S2; --输入不同,次态不同
ELSIF state_inputs=01 THEN next_state=S3;
ELSIF state_inputs=10 THEN next_state=S4;
END IF;
WHEN S3=>comb_outputs=10; --现态S3
IF state_inputs=00 THEN next_state=S0; --输入不同,次态不同
ELSIF state_inputs=01 THEN next_state=S1;
ELSIF state_inputs=10 THEN next_state=S2;
END IF;
WHEN S4=>comb_outputs=11; --现态S4
IF state_inputs=00 THEN next_state=S0; --输入不同,次态不同
ELSIF state_inputs=01 THEN next_state=S1;
ELSIF state_inputs=10 THEN next_state=S2;
END IF;
END CASE;
END PROCESS;
END state;
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