drink-st.v

design compile synthesis user guide

`define vend_a_drink {D,dispense,collect} = {IDLE,2'b11}

module drink_machine(nickel_in, dime_in, quarter_in,
                     collect, nickel_out, dime_out,
                     dispense, reset, clk) ;

   parameter IDLE=0,FIVE=1,TEN=2,TWENTY_FIVE=3,
             FIFTEEN=4,THIRTY=5,TWENTY=6,OWE_DIME=7;

   input  nickel_in, dime_in, quarter_in, reset, clk;
   output collect, nickel_out, dime_out, dispense;

   reg collect, nickel_out, dime_out, dispense; 
   reg [2:0] D, Q; /* state */

always @ ( nickel_in or dime_in or quarter_in or reset )
      begin
         nickel_out = 0;
         dime_out   = 0;
         dispense   = 0;
         collect    = 0;

         if ( reset ) D = IDLE;
         else begin
            D = Q;

            case ( Q )
            IDLE:     if (nickel_in)       D = FIVE;
                      else if (dime_in)    D = TEN;
                      else if (quarter_in) D = TWENTY_FIVE;

            FIVE:     if(nickel_in)        D = TEN;
                      else if (dime_in)    D = FIFTEEN;
                      else if (quarter_in) D = THIRTY;


            TEN:      if (nickel_in)       D = FIFTEEN;
                      else if (dime_in)    D = TWENTY;
                      else if (quarter_in) `vend_a_drink;

            TWENTY_FIVE: if( nickel_in)       D = THIRTY;
                      else if (dime_in)    `vend_a_drink;
                      else if (quarter_in) begin
                         `vend_a_drink;
                          nickel_out = 1;
                          dime_out = 1;
                      end

            FIFTEEN:  if (nickel_in)       D = TWENTY;
                      else if (dime_in)    D = TWENTY_FIVE;
                      else if (quarter_in) begin
                         `vend_a_drink;
                         nickel_out = 1;
                      end
 
            THIRTY:   if (nickel_in)       `vend_a_drink;
                      else if (dime_in)    begin
                         `vend_a_drink;
                         nickel_out = 1;
                      end
                      else if (quarter_in) begin
                         `vend_a_drink;
                         dime_out = 1;
                         D = OWE_DIME;
                      end
 
            TWENTY:   if (nickel_in)       D = TWENTY_FIVE;
                      else if (dime_in)    D = THIRTY;
                      else if (quarter_in) begin
                         `vend_a_drink;
                         dime_out = 1;
                      end
 
            OWE_DIME: begin
                      dime_out = 1;
                      D = IDLE;
                      end
            endcase
    end
end
always @ (posedge clk ) begin
     Q = D;
end
endmodule