题解 | #自动售卖机#

`timescale 1ns/1ns

module sale(
   input                clk   ,
   input                rst_n ,
   input                sel   ,//sel=0,5$dranks,sel=1,10&=$drinks
   input          [1:0] din   ,//din=1,input 5$,din=2,input 10$
 
   output   reg  [1:0] drinks_out,//drinks_out=1,output 5$ drinks,drinks_out=2,output 10$ drinks
   output	reg        change_out   
);
reg state,next_state;
always@(posedge clk or negedge rst_n)begin
    if(~rst_n)begin
        state<=0;
    end
    else begin
        state<=next_state;
    end
end
always@(*)begin
    case(state)
    0:next_state<=sel==1&din==1?1:0;
    1:next_state<=(sel==1&din==1)|(sel==1&din==2)?0:1;
    default:state<=0;
    endcase 
end
always@(posedge clk or negedge rst_n)begin
    if(~rst_n)begin
        drinks_out<=0;
    end
    else if(sel==0)begin
        drinks_out<=(state==0&din==1)|(state==0&din==2)?1:0;
    end
    else begin
        drinks_out<=(state==0&din==2)|(state==1&din==1)|(state==1&din==2)?2:0;
    end
end
always@(posedge clk or negedge rst_n)begin
    if(~rst_n)begin
        change_out<=0;
    end
    else if(sel==0)begin
        change_out<=(state==0&din==2)|(state==1&din==2)?1:0;
    end
    else begin
        change_out<=(state==1&din==2)?1:0;
    end
end
endmodule