状态机例子-自动售货机13页

1、 Digital System Design例：用三进程状态机实现一个简单自动售货机控制电路，电路框图如下。该电路有两个投币口（1元和5角），商品2元一件，不设找零。In0表示投入5角，In1表示投入1元，Out表示是否提供货品。自动售货机In0In1ClkResetOut自动售货机顶层结构框图根据题意，可分析出状态机的状态包括：S0（00001）：初始状态，未投币或已取商品S1（00010）：投币5角S2（00100）：投币1元S3（01000）：投币1.5元S4（10000）：投币2元或以上用独热码表示状态编码，如上所示。相应状态转换图如下（按Moore状态机设计）。xx/101/010/

2、010/001/001/0S1S0S4 S2 Reset自动售货机状态转换图10/0S301/0x1/0设计代码第一个Always块：状态转移。timescale 1ns/100psmodule saler_3always(Reset,Clk,In,Out);input Clk,Reset;input 1:0 In;output Out;reg Out;reg 4:0 state, next_state;parameter S0=5b00001, S1=5b00010, S2=5b00100, S3=5b01000,S4=5b10000;always (posedge Clk or posed

3、ge Reset)begin if (Reset) state=S0; else state=next_state;end第二个Always块：状态转移的组合逻辑条件判断92011/6/21 Computer Faculty of Guangdong University of Technologyalways (state or In)begin case(state) S0:begin if (In1) next_state=S2; else if(In0) next_state=S1; else next_state=S0; end S1:begin if (In1) next_stat

4、e=S3; else if(In0) next_state=S2; else next_state=S1; end S2:begin if (In1) next_state=S4; else if(In0) next_state=S3; else next_state=S2; end S3:begin if (In0|In1) next_state=S4; else next_state=S3; end S4:begin next_state=S0; end default:next_state=S0; endcaseend第三个Always块：输出组合逻辑always (state )beg

5、in case(state) S0:begin Out=0; end S1:begin Out=0; end S2:begin Out=0; end S3:begin Out=0; end S4:begin Out=1; end default:Out=0; endcaseendendmodule Digital System Design测试平台代码132011/6/21 Computer Faculty of Guangdong University of Technologytimescale 1ns/1nsmodule testbench_saler;reg clk,reset;reg 1:0 in;wire out;parameter DELY=20;saler_3always tb(.Clk(clk),.Reset(reset),.In(in),.Out(out);always #(DELY/2) clk = clk;initial begin clk=0; reset=0; #20 reset=1; #20 reset=0; endin