VGA Port CSE 678

Raster Scan Displays Electron beam CRT

Raster Scan Characters 14 9

T 54 H 48 Character E 45 generator Character line 1 Row (40 words or select 80 bytes) 1 1 1 1 1 0 0 0 Video Shift register signal Character line 2 (40 words or 80 bytes) even addresses odd addresses

Attribute Byte 7 6 5 4 3 2 1 0 BL R G B I R G B Blinking bit 7 6 5 4 3 2 1 0 BL R G B I R G B Blinking bit Foreground 0 = not blinking 1 = foreground Intensity bit blinking 0 = normal intensity 1 = high intensity Background

Back porch Back porch Front porch

Horizontal Timing 144 784 Pixel clock = 25 MHz Pixel time = 0.04 ms Horizontal video = 640 pixels x 0.04 ms = 25.60 ms Back porch, BP = 16 pixels x 0.04 ms = 0.64 ms Front porch, FP = 16 pixels x 0.04 ms = 0.64 ms Sync pulse, SP = 128 pixels x 0.04 ms = 5.12.ms Horizontal Scan Lines = SP + BP + HV + FP = 128 + 16 + 640 + 16 = 800 pixels x 0.04 ms = 32 ms 1/60 Hz = 16.67 ms / 32 ms = 521 horizontal scan lines per frame

Vertical Timing 31 511 Pixel clock = 25 MHz Horizontal scan time = 32 ms Vertical video = 480 pixels x 32 ms = 15.360 ms Back porch, BP = 29 pixels x 32 ms = 0.928 ms Front porch, FP = 10 pixels x 32 ms = 0.320 ms Sync pulse, SP = 2 pixels x 32 ms = 0.064 ms Horizontal Scan Lines = SP + BP + VV + FP = 2 + 29 + 480 + 10 = 521 pixels x 32 ms = 16.672 ms 1/60 Hz = 16.67 ms

VGA Controller entity vgaController is Port ( mclk, clr : in std_logic; hs : out std_logic; vs : out std_logic; red : out std_logic; grn : out std_logic; blu : out std_logic); end vgaController;

VGA Controller architecture Behavioral of vgaController is constant hpixels: std_logic_vector(9 downto 0) := "1100100000"; --Value of pixels in a horizontal line = 800 constant vlines: std_logic_vector(9 downto 0) := "1000001001"; --Number of horizontal lines in the display = 521 constant hbp: std_logic_vector(9 downto 0) := "0010010000"; --Horizontal back porch = 144 (128+16) constant hfp: std_logic_vector(9 downto 0) := "1100010000"; --Horizontal front porch = 784 (128+16+640) constant vbp: std_logic_vector(9 downto 0) := "0000011111"; --Vertical back porch = 31 (2+29) constant vfp: std_logic_vector(9 downto 0) := "0111111111"; --Vertical front porch = 511 (2+29+480) signal hc, vc: std_logic_vector(9 downto 0); --These are the Horizontal and Vertical counters

VGA Controller signal clkdiv : std_logic; --Clock divider signal vidon : std_logic; --Tells whether or not its ok to display data signal vsenable: std_logic; --Enable for the Vertical counter begin --This cuts the 50Mhz clock in half process(mclk, clr) if clr = '1' then clkdiv <= '0'; elsif(mclk = '1' and mclk'EVENT) then clkdiv <= not clkdiv; end if; end process;

VGA Controller --Runs the horizontal counter process(clkdiv) begin if clr = '1' then hc <= "0000000000"; elsif(clkdiv = '1' and clkdiv'EVENT) then if hc = hpixels then --If the counter has reached the end of pixel count hc <= "0000000000"; --reset the counter vsenable <= '1'; --Enable the vertical counter to increment else hc <= hc + 1; --Increment the horizontal counter vsenable <= '0'; --Leave the vsenable off end if; end process; hs <= '0' when hc(9 downto 7) = "000" else '1'; --Horizontal Sync Pulse is low when hc is 0 - 127

VGA Controller --Runs the vertical counter process(clkdiv) begin if clr = '1' then vc <= "0000000000"; elsif(clkdiv = '1' and clkdiv'EVENT and vsenable = '1') then --Increment when enabled if vc = vlines then --Reset when the number of lines is reached else vc <= vc + 1; --Increment the vertical counter end if; end process; vs <= '0' when vc(9 downto 1) = "000000000" else '1'; --Vertical Sync Pulse is low when vc is 0 or 1

VGA Controller red <= '1' when (hc = "1010101100" and vidon ='1') else '0'; --Red pixel on at a horizontal count = 684 = 144 + 540 grn <= '1' when (hc = "0100000100" and vidon ='1') else '0'; --Green pixel on at a horizontal count = 260 = 144 + 116 blu <= '1' when (vc = "0100100001" and vidon ='1') else '0'; --Blue pixel on at a vertical count = 289 = 31 + 258 vidon <= '1' when (((hc < hfp) and (hc > hbp)) and ((vc < vfp) and (vc > vbp))) else '0'; --Enable video out when within the porches end Behavioral;