Verilog HDL--VGA显示

module vga(
            clk,rst_n,
            hsync,vsync,
            vga_r,vga_g,vga_b
        );

input clk;        //50MHz
input rst_n;    //低电平复位
output hsync;    //行同步信号
output vsync;    //场同步信号
output vga_r;
output vga_g;
output vga_b;

//--------------------------------------------------
reg[10:0] x_cnt;    //行坐标
reg[9:0] y_cnt;    //列坐标

always @ (posedge clk or negedge rst_n)
    if(!rst_n) x_cnt <= 11'd0;
    else if(x_cnt == 11'd1039) x_cnt <= 11'd0;
    else x_cnt <= x_cnt+1'b1;

always @ (posedge clk or negedge rst_n)
    if(!rst_n) y_cnt <= 10'd0;
    else if(y_cnt == 10'd665) y_cnt <= 10'd0;
    else if(x_cnt == 11'd1039) y_cnt <= y_cnt+1'b1;

//--------------------------------------------------
wire valid;    //有效显示区标志

assign valid = (x_cnt >= 11'd187) && (x_cnt < 11'd987) 
                    && (y_cnt >= 10'd31) && (y_cnt < 10'd631); 

wire[9:0] xpos,ypos;    //有效显示区坐标

assign xpos = x_cnt-11'd187;
assign ypos = y_cnt-10'd31;

//--------------------------------------------------
reg hsync_r,vsync_r;    //同步信号产生

always @ (posedge clk or negedge rst_n)
    if(!rst_n) hsync_r <= 1'b1;
    else if(x_cnt == 11'd0) hsync_r <= 1'b0;    //产生hsync信号
    else if(x_cnt == 11'd120) hsync_r <= 1'b1;
 
always @ (posedge clk or negedge rst_n)
    if(!rst_n) vsync_r <= 1'b1;
    else if(y_cnt == 10'd0) vsync_r <= 1'b0;    //产生vsync信号
    else if(y_cnt == 10'd6) vsync_r <= 1'b1;

assign hsync = hsync_r;
assign vsync = vsync_r;

//--------------------------------------------------
    //显示一个矩形框
wire a_dis,b_dis,c_dis,d_dis;    //矩形框显示区域定位

assign a_dis = ( (xpos>=200) && (xpos<=220) ) 
                &&    ( (ypos>=140) && (ypos<=460) );
                
assign b_dis = ( (xpos>=580) && (xpos<=600) )
                && ( (ypos>=140) && (ypos<=460) );

assign c_dis = ( (xpos>=220) && (xpos<=580) ) 
                &&    ( (ypos>140)  && (ypos<=160) );
                
assign d_dis = ( (xpos>=220) && (xpos<=580) )
                && ( (ypos>=440) && (ypos<=460) );

    //显示一个小矩形
wire e_rdy;    //矩形的显示有效矩形区域

assign e_rdy = ( (xpos>=385) && (xpos<=415) )
                &&    ( (ypos>=285) && (ypos<=315) );

//-------------------------------------------------- 
    //r,g,b控制液晶屏颜色显示，背景显示蓝色，矩形框显示红蓝色
assign vga_r = valid ? e_rdy : 1'b0;
assign vga_g = valid ?  (a_dis | b_dis | c_dis | d_dis) : 1'b0;
assign vga_b = valid ? ~(a_dis | b_dis | c_dis | d_dis) : 1'b0;      

endmodule