自动售货机 

if朴素方法

 一种思路是用寄存器cnt记录已有的最小单位货币量，这里就是0.5

当d1时，cnt+1;d2时，cnt+2;d3时，cnt+4;

`timescale 1ns/1ns
module seller1(input wire clk  ,input wire rst  ,input wire d1 ,input wire d2 ,input wire d3 ,output reg out1,output reg [1:0]out2
);
reg[2:0]cnt;
always@(posedge clk,negedge rst)beginif(!rst)begincnt<=0;out1<=0;out2<=0;endelse beginif(d1)cnt<=cnt+1;else if(d2)cnt<=cnt+2;else if(d3)cnt<=cnt+4;else if(cnt>=3)beginout1<=1;out2<=cnt-3;cnt<=0;//记得复位为0，表示一个过程的结束endelse beginout1<=0;out2<=0;end//这里需要注意一定需要这一步，不然在不复位时，将保持一直输出1的状态end
end
endmodule

这里注意，d1,d2,d3都是以脉冲的形式，即只会接受一个时间步里，检测也都是

`timescale 1ns/1nsmodule seller1(input wire clk  ,input wire rst  ,input wire d1 ,input wire d2 ,input wire d3 ,output reg out1,output reg [1:0]out2
);parameter S0 = 'd0, S1 = 'd1, S2 = 'd2, S3 = 'd3 , S4 = 'd4, S5 = 'd5 , S6 = 'd6;reg  [2:0]	current_state;reg  [2:0]	next_state;wire [2:0]   input_state;//将输入组合起来assign input_state = {d1,d2,d3};always@(posedge clk or negedge rst)beginif(rst == 1'b0)begincurrent_state <= S0;endelse begincurrent_state <= next_state;endend   always@(*)begincase(current_state)S0:begincase(input_state)3'b100:next_state = S1 ;3'b010:next_state = S2 ;3'b001:next_state = S4 ;default:next_state = next_state;endcase	endS1:begincase(input_state)3'b100:next_state = S2 ;3'b010:next_state = S3 ;3'b001:next_state = S5 ;default:next_state = next_state; endcaseendS2:begincase(input_state)3'b100:next_state = S3 ;3'b010:next_state = S4 ;3'b001:next_state = S6 ;default:next_state = next_state;endcase				enddefault:beginnext_state = S0;endendcaseendalways@(posedge clk or negedge rst)beginif(rst == 1'b0)beginout1 <= 1'b0;out2 <= 2'b0;endelse begincase(next_state)S3:		   begin out1 <= 1'b1;out2 <= 2'b0; end S4:		   begin out1 <= 1'b1;out2 <= 2'b1; end S5:		   begin out1 <= 1'b1;out2 <= 2'b10; end S6:		   begin out1 <= 1'b1;out2 <= 2'b11; end default:   begin out1 <= 1'b0;out2 <= 2'b0; end endcase	endendendmodule

状态机方法

采用MOORE状态机，即输出只与状态有关，而与当前输入信号无关

状态机的方式可以支持一次投入多枚硬币

MOORE三段

第一段：信号声明，状态定义，状态转换

第二段：由现态，依据输入信号确定次态

这里可以看出，如果一次投入多个硬币，可以进行转移与判断，只需在case里增添判断即可

第三段：依据次态确定输出信号

自动售货机（支持多物品售卖）

sel为0时买一块五，即第四个状态，s3;为1时买两块五，为第六个状态，s5

状态机

`timescale 1ns/1nsmodule seller2(input wire clk  ,input wire rst  ,input wire d1 ,input wire d2 ,input wire sel ,output reg out1,output reg out2,output reg out3
);
//*************code***********//parameter S0=0, S0_5=1, S1=2, S1_5=3, S2=4, S2_5=5, S3=6;reg[2:0] state, nstate;always@(posedge clk or negedge rst) beginif(~rst)state <= 0;elsestate <= nstate;endalways@(*) begincase(state)S0     : nstate = d1? S0_5:d2? S1:nstate;S0_5   : nstate = d1? S1:d2? S1_5:nstate;S1     : nstate = d1? S1_5:d2? S2:nstate;S1_5   : nstate = ~sel? S0:d1? S2:d2? S2_5:nstate;S2     : nstate = ~sel? S0:d1? S2_5:d2? S3:nstate;default: nstate = S0;endcaseendalways@(*) beginif(~rst) begin{out1, out2, out3} = 3'b000;endelse begincase(state)S0, S0_5, S1: {out1, out2, out3} = 0;S1_5        : {out1, out2, out3} = ~sel? 3'b100: 3'b000;S2          : {out1, out2, out3} = ~sel? 3'b101: 3'b000;S2_5        : {out1, out2, out3} = ~sel? 3'b101: 3'b010;S3          : {out1, out2, out3} = ~sel? 3'b101: 3'b011;default     : {out1, out2, out3} = 3'b000;endcaseendend
//*************code***********//
endmodule

上面为mealy型状态机，即输出取决于现态与输入信号 

`timescale 1ns/1nsmodule seller2(input wire clk  ,input wire rst  ,input wire d1 ,input wire d2 ,input wire sel ,output reg out1,output reg out2,output reg out3
);parameter S0 = 'd0, S1 = 'd1, S2 = 'd2, S3 = 'd3 , S4 = 'd4, S5 = 'd5, S6 = 'd6;reg [2:0]	current_state;reg [2:0]	next_state;wire [1:0]  input_state;assign input_state = {d1,d2};always@(posedge clk or negedge rst)beginif(rst == 1'b0)begincurrent_state <= S0;endelse begincurrent_state <= next_state;endend   always@(*)beginif (!sel) begincase(current_state)S0:begincase(input_state)2'b10 :next_state = S1 ;2'b01 :next_state = S2 ;default:next_state = next_state;endcase	endS1:begincase(input_state)2'b10 :next_state = S2 ;2'b01 :next_state = S3 ;default:next_state = next_state;endcase	 endS2:begincase(input_state)2'b10 :next_state = S3 ;2'b01 :next_state = S4 ;default:next_state = next_state;endcase	enddefault:  next_state = S0;  endcaseendelse begincase(current_state)S0:begincase(input_state)2'b10 :next_state = S1 ;2'b01 :next_state = S2 ;default:next_state = next_state;endcase	endS1:begincase(input_state)2'b10 :next_state = S2 ;2'b01 :next_state = S3 ;default:next_state = next_state;endcase	 endS2:begincase(input_state)2'b10 :next_state = S3 ;2'b01 :next_state = S4 ;default:next_state = next_state;endcase	endS3:begincase(input_state)2'b10 :next_state = S4 ;2'b01 :next_state = S5 ;default:next_state = next_state;endcase	endS4:begincase(input_state)2'b10 :next_state = S5 ;2'b01 :next_state = S6 ;default:next_state = next_state;endcase	enddefault:  next_state = S0;  endcaseendendalways@(posedge clk or negedge rst)beginif(rst == 1'b0)beginout1 <= 1'b0;out2 <= 1'b0;out3 <= 1'b0;endelse beginif(!sel)begincase (next_state)S3:		begin out1 <= 1'b1;out2 <= 1'b0;out3 <= 1'b0;end S4:		begin out1 <= 1'b1;out2 <= 1'b0;out3 <= 1'b1;end default:begin out1 <= 1'b0;out2 <= 1'b0;out3 <= 1'b0;end endcaseendelse begincase (next_state)	S5:		begin out1 <= 1'b0;out2 <= 1'b1;out3 <= 1'b0;end 	S6:		begin out1 <= 1'b0;out2 <= 1'b1;out3 <= 1'b1;end 	default:begin out1 <= 1'b0;out2 <= 1'b0;out3 <= 1'b0;end 	endcase	endendendendmodule

上面为标准的MOORE状态机代码，即输出只与次态有关

在状态转换中，一定要记得写

即相当于 后面的复位，不然没办法复位