MicroBlaze Development Kit Spartan-3E 1600 Edition User Guide 55UG257 (v1.1) December 5, 2007 www.xilinx.comSignal Timing for a 60 Hz, 640x480 VGA DisplayRThe display resolution defines the size of the beams, the frequency at which the beamtraces across the display, and the frequency at which the electron beam is modulated.Modern VGA displays support multiple display resolutions, and the VGA controllerdictates the resolution by producing timing signals to control the raster patterns. Thecontroller produces TTL-level synchronizing pulses that set the frequency at which currentflows through the deflection coils, and it ensures that pixel or video data is applied to theelectron guns at the correct time.Video data typically comes from a video refresh memory with one or more bytes assignedto each pixel location. The MicroBlaze Development Kit board uses three bits per pixel,producing one of the eight possible colors shown in Table 6-1. The controller indexes intothe video data buffer as the beams move across the display. The controller then retrievesand applies video data to the display at precisely the time the electron beam is movingacross a given pixel.As shown in Figure 6-2, the VGA controller generates the horizontal sync (HS) and verticalsync (VS) timings signals and coordinates the delivery of video data on each pixel clock.The pixel clock defines the time available to display one pixel of information. The VS signaldefines the refresh frequency of the display, or the frequency at which all information on theFigure 6-2: CRT Display Timing ExampleCurrentthrough thehorizontaldeflectioncoilStable current ramp: Information isdisplayed during this timeRetrace: Noinformationis displayedduringthis timeTotal horizontal timeHorizontal display timeHorizontal sync signalsets the retrace frequencyretrace timetimeHS"back porch""front porch"VGA Display640 pixels are displayed eachtime the beam traverses the screenpixel 0,639pixel 0,0pixel 479,0 pixel 479,639"front porch"UG257_06_02_060506
