dot_top.v

// Listing 13.8
module dot_top
   (
    input wire clk, reset,
    input wire [1:0] btn,
    input wire [2:0] sw,
    output wire hsync, vsync,
    output wire [2:0] rgb
   );

   // signal declaration
   wire [9:0] pixel_x, pixel_y;
   wire video_on, pixel_tick;
   reg [2:0] rgb_reg;
   wire [2:0] rgb_next;

   // body
   // instantiate VGA sync circuit
   vga_sync vsync_unit
      (.clk(clk), .reset(reset), .hsync(hsync), .vsync(vsync),
       .video_on(video_on), .p_tick(pixel_tick),
       .pixel_x(pixel_x), .pixel_y(pixel_y));

   // instantiate graphic generator
   bitmap_gen bitmap_unit
      (.clk(clk), .reset(reset), .btn(btn), .sw(sw),
       .video_on(video_on), .pix_x(pixel_x),
       .pix_y(pixel_y), .bit_rgb(rgb_next));

   // rgb buffer
   always @(posedge clk)
      if (pixel_tick)
         rgb_reg <= rgb_next;
   // output
   assign rgb = rgb_reg;

endmodule