Vending_Machine

[NamDoanDinh]

Describe the bug
I don't know huhu
The code
`module vending_machine(
input clk,
input nickle, dime, quarter,
output reg soda,
output reg [3:0] change
);

//parameter for state assignment
parameter   S0  =  4'd0,            //soda = 0, change = 0
            S5  =  4'd1,            //soda = 0, change = 0
            S10 =  4'd2,            //soda = 0, change = 0
            S15 =  4'd3,            //soda = 0, change = 0                
            S20 =  4'd4,            //soda = 1, change = 0
            S25 =  4'd5,            //soda = 1, change = 5
            S30 =  4'd6,            //soda = 1, change = 10                
            S35 =  4'd7,            //soda = 1, change = 15               
            S40 =  4'd8;            //soda = 1, change = 20
//parameter for the change
parameter   C0  =  3'b000,          //change = 0
            C5  =  3'b001,          //change = 5
            C10 =  3'b010,          //change = 10
            C15 =  3'b011,          //change = 15
            C20 =  3'b100;          //change = 20        
                                 
reg [3:0] state, next_state;

//input equation (ref: state diagram)
always @(*) begin
      case (state)
      S0: case({nickle, dime, quarter})
      3'b100: next_state = S5;
      3'b010: next_state = S10;
      3'b001: next_state = S25;
      default: next_state = S0;
      endcase
      S5: case({nickle, dime, quarter})
      3'b100: next_state = S10;
      3'b010: next_state = S15;
      3'b001: next_state = S30;
      default: next_state = S5;          
      endcase
      S10: case({nickle, dime, quarter})
      3'b100: next_state = S15;
      3'b010: next_state = S20;
      3'b001: next_state = S35;
      default: next_state = S10;
      endcase     
      S15: case({nickle, dime, quarter})
      3'b100: next_state = S20;
      3'b010: next_state = S25;
      3'b001: next_state = S40;
      default: next_state = S15;
      endcase      
      S20: case({nickle, dime, quarter})
      3'b100: next_state = S5;
      3'b010: next_state = S10;
      3'b001: next_state = S25;
      default: next_state = S20;
      endcase      
      S25: case({nickle, dime, quarter})
      3'b100: next_state = S5;
      3'b010: next_state = S10;
      3'b001: next_state = S25;
      default: next_state = S25;          
      endcase  
      S30: case({nickle, dime, quarter})
      3'b100: next_state = S5;
      3'b010: next_state = S10;
      3'b001: next_state = S25;
      default: next_state = S30; 
      endcase      
      S35: case({nickle, dime, quarter})
      3'b100: next_state = S5;
      3'b010: next_state = S10;
      3'b001: next_state = S25;
      default: next_state = S35;          
      endcase   
      S40: case({nickle, dime, quarter})
      3'b100: next_state = S5;
      3'b010: next_state = S10;
      3'b001: next_state = S25;
      default: next_state = S40;
      endcase 
      default: next_state = state;
      endcase                          
end

//Seq logic
always @(posedge clk) begin
    state <= next_state;
end

//output equation
always @(*) begin
      case(state)
      S0:  begin soda = 0; change = C0; end
      S5:  begin soda = 0; change = C0; end
      S10: begin soda = 0; change = C0; end
      S15: begin soda = 0; change = C0; end               
      S20: begin soda = 1; change = C0; end
      S25: begin soda = 1; change = C5; end
      S30: begin soda = 1; change = C10; end
      S35: begin soda = 1; change = 15; end     
      S40: begin soda = 1; change = 20; end  
      default: begin soda = 0; change = C0; end            
      endcase
end

endmodule
`