Verilog Code for Vending Machine Using FSM

Sr. No.	Name of the Pin	Direction	Width	Description
1	Nw_pa	Output	1	News Paper Signal
2	Coin	Input	2	Only two Coins, 5 =2’b01 10 =2’b10 0 =2’b00
3	Clk	Input	1	Clock Signal
4	Rst	Input	1	Reset Signal

In this wending machine, it accepts only two coins, 5 point and 10 point. Whenever total of coins equal to 15 points, then nw_pa signal will go high and user will get news paper. It will not return any coin, if total of points exceeds 15 points.

Design Code

module vending_machine(nw_pa,clk,coin,rst);

   output reg nw_pa;
   input [1:0] coin;
   input       clk,rst;
   reg [1:0]   state;
   reg [1:0]   next_state;


   parameter [1:0] s0=2'b00;
   parameter [1:0] s5=2'b01;
   parameter [1:0] s10=2'b10;
   parameter [1:0] s15=2'b11;


   always @(posedge clk)
     begin
       if (rst)
         state=s0;
       else
         state=next_state;
     end


   always @(state,coin)
     begin
    case (state)
     s0:
        begin
           if (coin==2'b00)
        next_state=s0;
           else
       if (coin==2'b01)
          next_state=s5;
       else
         if (coin==2'b10)
          next_state=s10;
        end
       s5:
          begin
       if (coin==2'b00)
          next_state=s5;
       else
         if (coin==2'b01)
            next_state=s10;
         else
           if (coin==2'b10)
             next_state=s15;
             end
       s10:
          begin
           if (coin==2'b00)
        next_state=s10;
           else
       if (coin==2'b01)
          next_state=s15;
       else
        if (coin==2'b10)
            next_state=s15;  
           end
       s15:
          begin
       next_state=s0;
          end
       default : next_state=s0;
   
    endcase // case (state)
     end // always @ (state,next_state)


   always @(state)
 begin
   case (state)
      s0 : nw_pa<=1'b0;
      s5 : nw_pa<=1'b0;
      s10: nw_pa<=1'b0;
      s15: nw_pa<=1'b1;
    default: nw_pa<=1'b0;
   endcase // case (state)
 end
 
endmodule