VGA
Signal
Timing
A
single
dot
of
color
on
a
video
monitor
doesn’t
impart
much
information
.
A
horizontal
line
of
pixels
carries
a
bit
more
information
.
But
a
frame
composed
of
multiple
lines
can
present
an
image
on
the
monitor
screen
.
A
frame
of
VGA
video
typically
has
480
lines
and
each
line
usually
contains
640
pixels
.
In
order
to
paint
a
frame,
there
are
deflection
circuits
in
the
monitor
that
move
the
electrons
emitted
from
the
guns
both
left
-
to
-
right
and
top
-
to
-
bottom
across
the
screen
.
These
deflection
circuits
require
two
synchronization
signals
in
order
to
start
and
stop
the
deflection
circuits
at
the
right
times
so
that
a
line
of
pixels
is
painted
across
the
monitor
and
the
lines
stack
up
from
the
top
to
the
bottom
to
form
an
image
.
The
timing
for
the
VGA
synchronization
signals
is
shown
in
Figure
2
.
Negative
pulses
on
the
horizontal
sync
signal
demark
the
start
and
end
of
a
line
and
ensure
that
the
monitor
displays
the
pixels
between
the
left
and
right
edges
of
the
visible
screen
area
.
The
actual
pixels
are
sent
to
the
monitor
within
a
25
.
17
m
s
window
.
The
horizontal
sync
signal
drops
low
a
minimum
of
0
.
94
m
s
after
the
last
pixel
and
stays
low
for
3
.
77
m
s
.
A
new
line
of
pixels
can
begin
a
minimum
of
1
.
89
m
s
after
the
horizontal
sync
pulse
ends
.
So
a
single
line
occupies
25
.
17
m
s
of
a
31
.
77
m
s
interval
.
The
other
6
.
6
m
s
of
each
line
is
the
horizontal
blanking
interval
during
which
the
screen
is
dark
.
In
an
analogous
fashion,
negative
pulses
on
a
vertical
sync
signal
demark
the
start
and
end
of
a
frame
made
up
of
video
lines
and
ensure
that
the
monitor
displays
the
lines
between
the
top
and
bottom
edges
of
the
visible
monitor
screen
.
The
lines
are
sent
to
the
monitor
within
a
15
.
25
ms
window
.
The
vertical
sync
signal
drops
low
a
minimum
of
0
.
45
ms
after
the
last
line
and
stays
low
for
64
m
s
.
The
first
line
of
the
next
frame
can
begin
a
minimum
of
1
.
02
ms
after
the
vertical
sync
pulse
ends
.
So
a
single
frame
occupies
15
.
25
ms
of
a
16
.
784
ms
interval
.
The
other
1
.
534
ms
of
the
frame
interval
is
the
vertical
blanking
interval
during
which
the
screen
is
dark
.