Digilent 410-087P-KIT - Manual (Page 55)

Spartan-3E Starter Kit Board User Guide www.xilinx.com 55
UG230 (v1.0) March 9, 2006
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 Spartan-3E Starter 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.
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"
UG230_c6_02_021706