module keypad(keyval,y,x,clk);
    
    output [4:0] keyval; //返回的鍵值
    output [3:0] x;     //輸出，列坐標
    input  [3:0] y;     //輸入，行坐標
    input  clk;         //時鐘源
    
    reg [4:0] keyval;
    reg [3:0] x;
    
    parameter clkdiv="2048";  
    parameter S0=4'd0,      //狀態機
              S1=4'd1,
              S2=4'd2,
              Wait="4"'d3,
              R0=4'd8,
              R0Temp=4'd9,
              R1=4'd10,
              R1Temp=4'd11,
              R2=4'd12,
              R2Temp=4'd13,
              R3=4'd14,
              R3Temp=4'd15;
              
    reg [3:0] state;
    
    reg [11:0] cnt;                        //2.048MHz，分頻因子，分為1000Hz
    always @(posedge clk)
      cnt <= cnt==clkdiv ? 0 : cnt+1;
    
    reg clken;
    always @(posedge clk)
      clken <= cnt==clkdiv;
    
     always @(posedge clk)                 //鍵盤掃描部分
     if(clken)
       begin
       case(state)
           S0:              //判斷是否按鍵按下
             begin
             x<=4'b0000;
             state="S1";
             end
            S1:
             begin
             if(y==4'b1111)  //無按鍵，返回
             state="S0";
             else 
             x<=4'b0000;
             repeat(204800) @(posedge clk);  //延時100ms,消抖     
             state="S2";             
             end
            S2:
             begin
             if(y==4'b1111)
             state="S0";
             else
             state="R0Temp";                     
             end
            R0Temp:                              //掃描第一列
             begin
             x<=4'b1110;
             state="R0";
             end
            R0:
              case(y)
                  4'b1111:
                     state="R1Temp";
                  4'b0111:
                     begin 
                     keyval<=5'd1;
                     state="Wait";
                     end
                  4'b1011:
                     begin
                     keyval<=5'd5;
                     state="Wait";
                     end
                  4'b1101:
                     begin
                     keyval<=5'd9;
                     state="Wait";
                     end
                  4'b1110:
                     begin
                     keyval<=5'd13;
                     state="Wait";
                     end
                   default:
                      state="Wait";   
                   endcase
               R1Temp:                              //掃描第二列
                begin
                x<=4'b1101;
                state="R1";
                end
               R1:
                 case(y)
                  4'b1111:
                     state="R2Temp";
                  4'b0111:
                     begin 
                     keyval<=5'd2;
                     state="Wait";
                     end
                  4'b1011:
                     begin
                     keyval<=5'd6;
                     state="Wait";
                     end
                  4'b1101:
                     begin
                     keyval<=5'd10;
                     state="Wait";
                     end
                  4'b1110:
                     begin
                     keyval<=5'd14;
                     state="Wait";
                     end
                   default:
                      state="Wait";   
                    endcase
              R2Temp:                                   //掃描第三列
               begin
               x<=4'b1011;
               state="R2";
               end
               R2:
               case(y)
                  4'b1111:
                     state="R3Temp";
                  4'b0111:
                     begin 
                     keyval<=5'd3;
                     state="Wait";
                     end
                  4'b1011:
                     begin
                     keyval<=5'd7;
                     state="Wait";
                     end
                  4'b1101:
                     begin
                     keyval<=5'd11;
                     state="Wait";
                     end
                  4'b1110:
                     begin
                     keyval<=5'd15;
                     state="Wait";
                     end
                   default:
                     state="Wait";   
                   endcase
             R3Temp:                                //掃描第四列
               begin
               x<=4'b0111;
               state="R3";
               end
             R3:
               case(y)
                  4'b1111:
                     state="Wait";
                  4'b0111:
                     begin 
                     keyval<=5'd4;
                     state="Wait";
                     end
                  4'b1011:
                     begin
                     keyval<=5'd8;
                     state="Wait";
                     end
                  4'b1101:
                     begin
                     keyval<=5'd12;
                     state="Wait";
                     end
                  4'b1110:
                     begin
                     keyval<=5'd16;
                     state="Wait";
                     end
                   default:
                      state="Wait"; 
                   endcase
                Wait:                                      //返回S0狀態
                   state="S0";  
                endcase
           end 
        
endmodule