vgasyncgen.vhd

描述：LED示范、按钮及开关、视频输出、键入、含Xilinx PicoBlaze微处理器的存储器模块

--Syncron generator for VGA 640x480@60Hz. 
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity VGASyncGen is
    Port ( CLK : in std_logic; --50 MHz clock
           HS : out std_logic;
           VS : out std_logic;
           VIDEO_ON : out std_logic; --Shoul only display pixels while this
			  	--is 1
           X : out std_logic_vector(9 downto 0);
           Y : out std_logic_vector(9 downto 0));
end VGASyncGen;

architecture Behavioral of VGASyncGen is

signal Pixel_Clock: std_logic;
signal horiz_sync, vert_sync : std_logic;
signal h_count, v_count: std_logic_vector(9 DOWNTO 0);
signal video_on_v, video_on_h : std_logic;

begin
	HS <= horiz_sync;
	VS <= vert_sync;
	VIDEO_ON <= video_on_v and video_on_h;

	--Divide the clock in half to get 50MHz
	process (CLK)
	begin
		if (CLK'event) and (CLK = '1') then
			Pixel_Clock <= not(Pixel_Clock);
		end if;
	end process;
	
	process (Pixel_Clock)
	begin
		if (Pixel_Clock'event) and (Pixel_Clock = '0') then
			--The horizontal pixel counter
			if (h_count >= 799) then
   			h_count <= (others => '0');
			else
   			h_count <= h_count + 1;
			end if;

			--The horizontal sync pulse
			if (h_count <= 755) and (h_count >= 659) then
 	  			horiz_sync <= '0';
			else
 	  			horiz_sync <= '1';
			end if;

			--Reset the vertical counter when appropiate
			--(maximum number of lines reached)
			if (v_count >= 524) and (h_count >= 699) then
   			v_count <= (others => '0');
			elsif (h_count = 699) then
   			v_count <= v_count + 1;
			end if;	

			--Vertical synch pulse (measured in lines, not pixels!)
			if (v_count <= 494) and (v_count >= 493) then
   			vert_sync <= '0';
			else
  				vert_sync <= '1';
			end if;

			--When appropiate, propageate the pixel / line count
			if (h_count <= 639) then
   			video_on_h <= '1';
   			X <= h_count;
			else
	   		video_on_h <= '0';
			end if;

			if (v_count <= 479) then
   			video_on_v <= '1';
   			Y <= v_count;
			else
   			video_on_v <= '0';
			end if;
		end if;
	end process;
end Behavioral;