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R
Current
through the
horizontal
deflection
coil
time
"front porch"
HS
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 Spartan-3E Starter Kit board uses three bits per pixel, producing
one of the eight possible colors shown in
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.
Spartan-3E Starter Kit Board User Guide
UG230 (v1.0) March 9, 2006
pixel 0,0
640 pixels are displayed each
time the beam traverses the screen
VGA Display
pixel 479,0
Stable current ramp: Information is
displayed during this time
Total horizontal time
Horizontal display time
Horizontal sync signal
sets the retrace frequency
Figure 6-2: CRT Display Timing Example
www.xilinx.com
Signal Timing for a 60 Hz, 640x480 VGA Display
pixel 0,639
pixel 479,639
retrace time
"back porch"
Table
6-1. The controller indexes into the video
Retrace: No
information
is displayed
during
this time
"front porch"
UG230_c6_02_021706
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