vga_vhdl.vhd

VGA格式输出,可直接接VGA专用芯片.可以输出不同的颜色,位置.

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

library UNISIM;
use UNISIM.VComponents.all;

entity vga is
    Port ( reset_display   : in  std_logic;  
    
	        video_clk, test_clk	           : out std_logic;
		     vga_hsyncb,vga_vsyncb            : out std_logic;	
		     dvd_psave, vga_blank, vga_csync  : out std_logic;	
		
		     red,gre,blu: out std_logic_vector(7 downto 0) );
end vga;

architecture vga_arch of vga is

signal cnt,cnt_div  : std_logic_vector(1 downto 0);	-- user pixel counter

signal hcnt  : std_logic_vector(8 downto 0);	-- horizontal pixel counter
signal vcnt  : std_logic_vector(9 downto 0);	-- vertical line counter
signal pixrg : std_logic_vector(7 downto 0);	-- byte-wide register for 4 pixels

signal clock : std_logic;
signal hsyncb: std_logic;	-- horizontal (line) sync
signal vsyncb: std_logic;	-- vertical (frame) sync
		
signal blank : std_logic;	-- video blanking signal
signal pblank: std_logic;	-- pipelined video blanking signal

signal reset :	std_logic;

begin

   vga_hsyncb <= hsyncb;
	vga_vsyncb <= vsyncb;
	
   dvd_psave <= '1' ; 
   vga_csync <= '0' ; 
   vga_blank <= '1' ;
	
	clock     <= cnt_div(1);
   video_clk <= cnt_div(1);

vga_rst : process(clock,reset_display)
   begin
	  if              reset_display='1' then cnt <= "00";
	  elsif (clock'event and clock='1') then cnt <= cnt + 1;
	  end if;
end process;

vga_div: process(clk,reset_display)
   begin
	  if           reset_display='1' then cnt_div <= "00";
	  elsif (clk'event and clk ='1') then cnt_div <= cnt_div + 1;
	  end if;
end process;
	
A: process(clock,reset_display)
   begin
 	  if reset_display='1' then   hcnt <= "000000000";
	  elsif (clock'event and clock='1') then
		 -- horiz. pixel counter rolls-over after 381 pixels
		 if hcnt<380 then hcnt <= hcnt + 1;
		 else	            hcnt <= "000000000";
		 end if;
	  end if;
end process;

B: process(hsyncb,reset_display)
  begin
	 if reset_display='1' then  vcnt <= "0000000000";
	 elsif (hsyncb'event and hsyncb='1') then
		-- vert. line counter rolls-over after 528 lines
		if vcnt<527 then  vcnt <= vcnt + 1;
		else			      vcnt <= "0000000000";
		end if;
	 end if;
end process;

C: process(clock,reset_display)
begin
	if reset_display='1' then hsyncb <= '1';
	elsif (clock'event and clock='1') then
		-- horiz. sync is low in this interval to signal start of a new line
		if (hcnt>=291 and hcnt<337) then  hsyncb <= '0';
		else                      			 hsyncb <= '1';
		end if;
	end if;
end process;

D: process(hsyncb,reset_display)
  begin
	 if reset_display='1' then  vsyncb <= '1';
	 elsif (hsyncb'event and hsyncb='1') then
		-- vert. sync is low in this interval to signal start of a new frame
		if (vcnt>=490 and vcnt<492) then vsyncb <= '0';
		else                    			vsyncb <= '1';
		end if;
	end if;
end process;


-- blank video outside of visible region: (0,0) -> (255,479)
E: blank <= '1' when (hcnt>=256 or vcnt>=480) else '0';


-- store the blanking signal for use in the next pipeline stage
F: process(clock,reset_display)
   begin
	  if              reset_display='1' then pblank <= '0';
	  elsif (clock'event and clock='1') then pblank <= blank;
	  end if;
end process;


-- the color mapper translates each 2-bit pixel into a 6-bit
-- color value.  When the video signal is blanked, the color
-- is forced to zero (black).
J: process(clock,reset_display)
begin
	-- blank the video on reset
	if reset_display='1' then 
		red <= "00000000"; gre <= "00000000"; blu <= "00000000";
	-- update the color outputs on every dot clock
	elsif (clock'event and clock='1') then
		-- map the pixel to a color if the video is not blanked
		if pblank='0' then
			case cnt is
				when "00" =>   red <= "11110000"; gre <= "00000000"; blu <= "00000000";	
				when "01" =>   red <= "00000000"; gre <= "11110000"; blu <= "00000000"; 
				when "10" =>   red <= "00000000"; gre <= "00000000"; blu <= "11110000";	
				when others => red <= "11111111"; gre <= "11111111"; blu <= "11111111";	-- white
			end case;
		-- otherwise, output black if the video is blanked
		else red <= "00000000"; gre <= "00000000"; blu <= "00000000"; -- black
		end if;
	end if;
end process;


end vga_arch;