1 Display Technology  Images stolen from various locations on the web... Cathode Ray Tube Cathode Ray Tube Raster Scanning Electron Gun Beam Steering Coils2 Color Shadow Mask and Aperture Grille Liquid Crystal Displays Liquid Crystal Displays DLP Projector LCoS  Liquid Crystal on Silicon  Put a liquid crystal between a reflective layer on a silicon chip3 Grating Light Valve (GLS)  lots (8000 currently) of micro ribbons that can bend slightly  Make them reflective  The bends make a diffraction grating that controls how much light where  Scan it with a laser for high light output  4000 pixel wide frame ever 60Hz Grating Light Valve (GLS) Digistar 3 Dome Projector VGA  Stands for Video Graphics Array  A standard defined by IBM back in 1987  640 x 480 pixels  Now superseded by much higher resolution standards...  Also means a specific analog connector  15-pin D-subminiature VGA connector The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.VGA Connector 1: Red out 6: Red return (ground) 11: Monitor ID 0 in 2: Green out 7: Green return (ground) 12: Monitor ID 1 in or data from display 3: Blue out 8: Blue return (ground) 13: Horizontal Sync 4: Unused 9: Unused 14: Vertical Sync 5: Ground 10: Sync return (ground) 15: Monitor ID 3 in or data clock Raster Scanning4 Raster Scanning “back porch” “back porch” “back porch” “front porch” VGA Timing Horizonal Dots 640 Vertical Scan Lines 480 Horiz. Sync Polarity NEG A (µs) 31.77 Scanline time B (µs) 3.77 Sync pulse length C (µs) 1.89 Back porch D (µs) 25.17 Active video time E (µs) 0.94 Front porch ______________________ ________ ________| VIDEO |________| VIDEO (next line) |-C-|----------D-----------|-E-| __ ______________________________ ___________ |_| |_| |B| |---------------A----------------| 60Hz vertical frequency VGA Timing Horizonal Dots 640 Vertical Scan Lines 480 Horiz. Sync Polarity NEG A (µs) 31.77 Scanline time B (µs) 3.77 Sync pulse length C (µs) 1.89 Back porch D (µs) 25.17 Active video time E (µs) 0.94 Front porch ______________________ ________ ________| VIDEO |________| VIDEO (next line) |-C-|----------D-----------|-E-| __ ______________________________ ___________ |_| |_| |B| |---------------A----------------| 60Hz vertical frequency 25.17/640 = 39.33ns/pixel = 25.4MHz pixel clock VGA Timing Horizonal Dots 640 Vertical Scan Lines 480 Vert. Sync Polarity NEG Vertical Frequency 60Hz O (ms) 16.68 Total frame time P (ms) 0.06 Sync pulse length Q (ms) 1.02 Back porch R (ms) 15.25 Active video time S (ms) 0.35 Front porch ______________________ ________ ________| VIDEO |________| VIDEO (next frame) |-Q-|----------R-----------|-S-| __ ______________________________ ___________ |_| |_| |P| |---------------O----------------| VGA Timing Summary 60 Hz refresh and 25MHz pixel clock Relaxed VGA Timing  This all sounds pretty strict and exact...  It’s not really... The only things a VGA monitor really cares about are:  Hsync  Vsync  Actually, all it cares about is the falling edge of those pulses!  The beam will retrace whenever you tell it to  It’s up to you to make sure that the video signal is 0v when you are not painting (i.e. retracing)5 Relaxed VGA Timing Horizonal Dots 128 Vertical Scan Lines ? Horiz. Sync Polarity NEG A (µs) 30.0 Scanline time B (µs) 2.0 Sync pulse length C (µs) 10.7 Back porch D (µs) 12.8 Active video time E (µs) 4.50 Front porch ______________________ ________ ________| VIDEO |________| VIDEO (next line) |-C-|----------D-----------|-E-| __ ______________________________ ___________ |_| |_| |B| |---------------A----------------| 60Hz vertical frequency 12.8/128 = 100ns/pixel = 10 MHz pixel clock VGA Timing Horizonal Dots 128 Vertical Scan Lines 255 Vert. Sync Polarity NEG Vertical Frequency 60Hz O (ms) 16.68 Total frame time P (ms) 0.09 Sync pulse length (3x30µs) Q (ms) 4.86 Back porch R (ms) 7.65 Active video time S (ms) 4.08 Front porch ______________________ ________ ________| VIDEO |________| VIDEO (next frame) |-Q-|----------R-----------|-S-| __ ______________________________ ___________ |_| |_| |P| |---------------O----------------| VGA Voltage Levels  Voltages on R, G, and B determine the color  Analog range from 0v (off) to +0.7v (on)  But, our pads produce 0-3.3v outputs! VGA Voltage Levels  Voltages on R, G, and B determine the color  Analog range from 0v (off) to +0.7v (on)  But, our pads produce 0-3.3v outputs!  For B&W output, just drive RGB together and let 0v=black and 3.3v=white  overdrives the input amps, but won’t really hurt anything  For color you can drive R, G, B separately  Of course, this is only 8 colors (including black and white)  Requires storing three bits at each pixel location VGA on Spartan3e Starter Series resistors limit output voltage to 0-0.7v VGA on Spartan3e Starter6 Raster Scanning “back porch” “back porch” “back porch” “front porch” VGA on Spartan3e Starter VGA on Spartan3e Starter VGA Assignment  vgaControl  Generate timing pulses at the right time  hSync, vSync, bright, hCount, vCount  bitGen  Based on bright, hCount, vCount, turn on