Vending_Machine.v

`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Company: NIT Warangal
// Engineer: Prakash Sharma
// 
// Create Date: 23.07.2023 01:49:38
// Design Name: 
// Module Name: Vending_Machine
// Project Name: Vending Machine Controller Using Verilog HDL
// Target Devices: 
// Tool Versions: 
// Description: 
// 
// Dependencies: 
// 
// Revision:
// Revision 0.01 - File Created
// Additional Comments:
// 
//////////////////////////////////////////////////////////////////////////////////

module VendingMachine(
    input clk,                    // Clock signal
    input rst,                    // Reset signal
    input [2:0] product_code,     // Product selection input signal
    input online_payment,         // Online payment signal
    input start,                  // Start signal
    input cancel,                 // Cancel signal
    input [6:0] total_coin_value, // Single coin input representing the total value of coins inserted

    output reg [3:0] state,               // Output signal to indicate the current state
    output reg dispense_product,         // Output signal to dispense the product
    output reg [6:0] return_change,      // Output signal to return the change
    output reg [6:0] product_price       // Output signal to indicate the price of the selected product
);

// Internal states of the vending machine
localparam IDLE_STATE = 4'b0000;
localparam SELECT_PRODUCT_STATE = 4'b0001;
localparam PEN_SELECTION_STATE = 4'b0010;
localparam NOTEBOOK_SELECTION_STATE = 4'b0011;
localparam COKE_SELECTION_STATE = 4'b0100;
localparam LAYS_SELECTION_STATE = 4'b0101;
localparam WATER_BOTTLE_SELECTION_STATE = 4'b0110;
localparam DISPENSE_AND_RETURN_STATE = 4'b0111;

// Parameters for product prices
parameter WATER_BOTTLE_PRICE = 7'd20;
parameter LAYS_PRICE = 7'd35;
parameter COKE_PRICE = 7'd30;
parameter PEN_PRICE = 7'd15;
parameter NOTEBOOK_PRICE = 7'd50;

// Internal signals
reg [3:0] current_state;
reg [3:0] next_state;
reg [6:0] product_price_reg;
reg [6:0] return_change_reg;

// Sequential State Registers
always @(posedge clk or posedge rst) begin
    if (rst) begin
        current_state <= IDLE_STATE;
        product_price_reg <= 0;
        return_change_reg <= 0;
    end else begin
        current_state <= next_state;
        product_price_reg <= product_price_reg; // No change during the same state
        return_change_reg <= return_change_reg; // No change during the same state
    end
end

// State transition logic
always @(*) begin
    case (current_state)
        IDLE_STATE: begin
            if (start)
                next_state = SELECT_PRODUCT_STATE;
            else if (cancel)
                next_state = IDLE_STATE;
            else 
                next_state = IDLE_STATE;
        end    
        SELECT_PRODUCT_STATE: begin
            case (product_code)
                3'b000: begin
                    next_state = PEN_SELECTION_STATE; // Pen is selected
                    product_price_reg = PEN_PRICE;
                end
                3'b001: begin
                    next_state = NOTEBOOK_SELECTION_STATE; // Notebook is selected
                    product_price_reg = NOTEBOOK_PRICE;
                end
                3'b010: begin
                    next_state = COKE_SELECTION_STATE; // Coke is Selected
                    product_price_reg = COKE_PRICE;
                end
                3'b011: begin
                    next_state = LAYS_SELECTION_STATE; // Lays is selected
                    product_price_reg = LAYS_PRICE;
                end
                3'b100: begin
                    next_state = WATER_BOTTLE_SELECTION_STATE; // Water bottle is selected
                    product_price_reg = WATER_BOTTLE_PRICE;
                end
                default: begin
                    next_state = IDLE_STATE; // Invalid product selection, go back to IDLE
                    product_price_reg = 0;
                end
            endcase
        end
        PEN_SELECTION_STATE, NOTEBOOK_SELECTION_STATE, COKE_SELECTION_STATE, LAYS_SELECTION_STATE, WATER_BOTTLE_SELECTION_STATE: begin
            if (cancel) begin 
                next_state = IDLE_STATE;
                return_change_reg = total_coin_value;
            end
            else if (total_coin_value >= product_price_reg)
                next_state = DISPENSE_AND_RETURN_STATE;
            else if (online_payment)
                next_state = DISPENSE_AND_RETURN_STATE;
            else
                next_state = current_state; // Stay in the current state until enough money or online payment
        end
        DISPENSE_AND_RETURN_STATE: begin
            next_state = IDLE_STATE;
            if (online_payment)
                return_change_reg = 0; // No return change in case of online payment
            else if (total_coin_value >= product_price_reg)
                return_change_reg = total_coin_value - product_price_reg;
        end
    endcase
end

// Output logic
always @(*) begin
    state = current_state;
    case (current_state)
        DISPENSE_AND_RETURN_STATE: begin
            dispense_product = 1;
            return_change = return_change_reg;
            product_price = product_price_reg;
        end
        default: begin
            dispense_product = 0;
            return_change = 0;
            product_price = 0; // Set to 0 when not in DISPENSE_AND_RETURN_STATE
        end
    endcase
end

endmodule