Slide Number 1VGA GraphicsCathode Ray TubeCathode Ray TubeScanningScanningVGA SignalingVGA TimingHorizontal Timing TermsVGA Timing (640 dots x 480 lines) Horizontal Sync Timing Vertical Sync TimingOther resolutionsVGA_SYNC ModuleVGA sync TimingOther Digital OutputsVGA LinksDepartment of Electrical and Computer EngineeringMississippi State UniversitySherif Abdelwahed VGA Graphics Computer Aided Digital Systems Design - EE 4743/6743VGA Graphics Based on Analog Monitors Has three color components (Red, Green, Blue) Analog Voltage determines intensity of each color for each pixel¾ 0.0V is darkest, 0.7V is brightest Combination creates 8 specific pixel colorsColor RGBBlack 000Blue 001Green 010Cyan 011Red 100Purple 101Yellow 110White 111Cathode Ray Tube Uses a beam of electrons to illuminate phosphor on the glass Only illuminates one pixel at a time Each pixel is only illuminated for 40ns (for 640x480 resolution) Beam is scanned across the display Left to right  Beam must reset back to the left at the end of each row At the bottom, it must go back up to the topCathode Ray TubeScanning Electron beam scans across Turned off when¾ Scanning back to the left (horizontal retrace)¾ Scanning to the top (vertical retrace) TVs use interlacing¾ Every other scan line is swept per field¾ Two fields per frame (30Hz)¾ Way to make movement less disturbing Computers use progressive scan¾ Whole frame refreshed at once¾ 60Hz or more, 72Hz looks betterScanning When the signal is resetting to the left side (or top) it is called Blanking The beam should be turned off at that time (drawing black) Significant time is lost when it could be drawing new pixels Specific signals used to tell the monitor when to return to the left and top (Sync signals)¾ Vertical Sync and Horizontal Sync¾ Automatically generated by moduleVGA SignalingThe five standard VGA signals Red, Green, Blue, Horizontal Sync (HS), and Vertical Sync (VS) are routed directly from the FPGA to the VGA connectorVGA Timing You supply two pulses, hsync and vsync, that let the monitor lock onto timing One hsync per scan line One vsync per frameHorizontal Timing Terms hsync pulse Back porch (left side of display) Active Video¾ Video should be blanked (not sent) at other times Front porch (right side)VGA Timing (640 dots x 480 lines)  Horizontal Sync = 31.5 Khz, Vertical Sync = 60 Hz Internal Monitor clock (Dot Clock) for latching video signal is 25.175 Mhz #max dots per line = Dot Clock Freq/ Horizontal Sync= 25.175 Mhz / 31.5 Khz = 800 Dots Only can use 640 dot times out of possible 800 for display because we need black areas on left/right edges and time for horizontal retrace.  #max lines per screen = Horizontal Sync/Vertical Sync = 31.5 Khz / 60 hz = 525 lines Only 480 lines usable, need blank areas on top/bottom, time for vertical retraceHorizontal Sync Timing 659 755756 7990 639 640659 75531.75 us (31.5 Khz)Horizontal retraceLeft BorderDisplayRight BorderNext Line800 dot times per lineCounter can be used to keep track of horizontal screen position.Vertical Sync Timing493 494495 5240 479 480493 49416.67 ms ( 60 hz)Vertical retraceTop BorderDisplayBottom BorderNext Screen525 line times per screenCounter can be used to keep track of vertical screen position.Other resolutions 800 x 600¾ Dot clock 36 Mhz¾ Horizontal Sync 35.15 Khz¾ Vertical Sync 56 hz 1024 x 768¾ Dot clock 64.142 Mhz¾ Horizontal Sync 48.3 Khz¾ Vertical Sync 60 hz Allow about 20% of horizontal trace time for borders, retrace 6% to 8% of vertical trace time for borders, retraceVGA_SYNC Module Provided module will automatically compute sync signals Will output Row(9:0) and Col(9:0) for which pixel it is drawing Can use this information to determine what color that pixel should be Many methods to determine color¾ Computationally (Lab 5)¾ Video Ram (Lab 6)¾ Hybrid (Lab 6)VGA sync Timing The following table shows the timing for a 640-pixel by 480-row display using a 25MHz pixel clock and 60 +/-1Hz refresh.Other Digital Outputs Newer methods for transmitting digital video information¾ DVI (Digital Visual Interface)¾ HDMI (High-Definition Multimedia Interface)¾ HDCP (High-Bandwidth Digital Content Protection) Ideal for digital displays (LCD Monitors & High-Definition Televisions) Each pixel has a specific digital color value FCC and MIAA prefer digital  Are the expected standard by 2007-2010 Opencores.org has a Wishbone compliant DVI generatorVGA Links VGA Timing¾ http://www.epanorama.net/documents/pc/vga_timing.html¾ http://appsrv.cse.cuhk.edu.hk/~ceg3480/Tutorial7/tut7.doc Code (more complex than you want)¾ http://www.stanford.edu/class/ee183/index.shtml Interesting¾ http://www.howstuffworks.com/tv.htm¾ http://computer.howstuffworks.com/monitor.htm¾ http://www.howstuffworks.com/lcd.htm¾ http://plc.cwru.edu/¾ Liquid Crystals by S. Chandrasekhar, Cambridge Univ.