Xilinx MIcroblaze Development Spartan-3E 1600E - Manual (Page 57)

MicroBlaze Development Kit Spartan-3E 1600 Edition User Guide 55
UG257 (v1.1) December 5, 2007 www.xilinx.com
Signal Timing for a 60 Hz, 640x480 VGA Display R
The display resolution defines the size of the beams, the frequency at which the beam
traces across the display, and the frequency at which the electron beam is modulated.
Modern VGA displays support multiple display resolutions, and the VGA controller
dictates the resolution by producing timing signals to control the raster patterns. The
controller produces TTL-level synchronizing pulses that set the frequency at which current
flows through the deflection coils, and it ensures that pixel or video data is applied to the
electron guns at the correct time.
Video data typically comes from a video refresh memory with one or more bytes assigned
to 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 into
the video data buffer as the beams move across the display. The controller then retrieves
and applies video data to the display at precisely the time the electron beam is moving
across a given pixel.
As shown in
Figure 6-2 , the VGA controller generates the horizontal sync (HS) and vertical
sync (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 signal
defines the refresh frequency of the display, or the frequency at which all information on the
Figure 6-2: CRT Display Timing Example
Current
through the
horizontal
deflection
coil
Stable current ramp: Information is
displayed during this time
Retrace: No
information
is displayed
during
this time
Total horizontal time
Horizontal display time
Horizontal sync signal
sets the retrace frequency
retrace time
time
HS
"back porch"
"front porch"
VGA Display
640 pixels are displayed each
time the beam traverses the screen
pixel 0,639 pixel 0,0
pixel 479,0
pixel 479,639
"front porch"
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