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
C
u
rrent
thro
u
gh the
horizont
a
l
deflection
coil
S
t
ab
le c
u
rrent r
a
mp: Inform
a
tion i
s
di
s
pl
a
yed d
u
ring thi
s
time
Retr
a
ce: No
inform
a
tion
i
s
di
s
pl
a
yed
d
u
ring
thi
s
time
Tot
a
l horizont
a
l time
Horizont
a
l di
s
pl
a
y time
Horizont
a
l
s
ync
s
ign
a
l
s
et
s
the retr
a
ce fre
qu
ency
retr
a
ce time
time
H
S
"
ba
ck porch"
"front porch"
VGA Di
s
pl
a
y
640 pixel
s
a
re di
s
pl
a
yed e
a
ch
time the
b
e
a
m tr
a
ver
s
e
s
the
s
creen
pixel 0,6
3
9
pixel 0,0
pixel 479,0
pixel 479,6
3
9
"front porch"
UG257_06_02_060506
