Xilinx LogiCORE IP, User Manual

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Video Scaler v4.0 User Guide www.xilinx.com 39
UG805 March 1, 2011
Chapter 7
Scaler Aperture
This section explains how to define the scaler aperture using the appropriate dynamic
control registers. The aperture is defined relative to the input timing signals.
Input Aperture Definition
It is vital to understand how to specify the scaler aperture properly. The scaler aperture is
defined as the input data rectangle used to create the output data rectangle. The input
values
aperture_start_line
,
aperture_end_line
,
aperture_start_pixel
and
aperture_end_pixel
need to be driven correctly.
To scale from a rectangle of size 1280x720, they should be set as follows:
It is also important to understand how “line 0” and “pixel 0” are defined to ensure that
these values are entered correctly. Line 0 is defined as the first active line following a rising
edge in
active_video_in
. An internal line counter is decoded to signal internally that
the current line is indeed line 0. This line counter is reset on a falling edge of
vblank_in
.
It increments on a rising edge of
hblank_in
.
One situation that needs to be avoided is the counter effectively starting at 1 instead of 0.
This will cause no video output. The correct relationship between input
hblank_in
and
vblank_in
to avoid this situation is shown in Figure 7-1 . The falling edge of
vblank_in
occurs while
hblank_in
is still high.
aperture_start_pixel 0
aperture_end_pixel 1279
aperture_start_line 0
aperture_end_line 719
X-Ref Target - Figure 7-1
Figure 7-1: Hblank_in at Falling Edge of VBlank_in