3.0 PC Board Considerations
CX25870/871
3.6 Applications Information
Flicker-Free Video Encoder with Ultrascale Technology
When the Adaptive Flicker Filter is on, the Standard Flicker Filter continues to
work normally. Indeed, many of the lines and/or pixels will still be filtered at the
more moderate standard flicker filter level. However, as the encoder analyzes and
processes each pixel, it will periodically come across certain regions requiring a
more aggressive filter setting. For these areas only, more forceful Adaptive
Flicker Filter value is used. With the dynamic ability of the CX25870, the
end-user can enjoy an optimal TV Out environment without having to manually
adjust the amount of flicker filtering depending on his given application. The
CX25870 provides this functionality so long as the Adaptive Flicker Filter slider
and control boxes are included. When the adaptive element is turned on, an
additional five flicker reduction settings can be applied by moving the control pad
to another level.
Through testing, Conexant recommends the following bit settings get
reprogrammed according to the state of the Adaptive Flicker Filter slider.
Integrating both flicker filter sliders and the correct intelligence behind them
makes the CX25870/871 ideal for Internet browsing, DVD movie watching, or
game playing by overcoming many of the quality problems like image flicker,
illegible text, and low-definition graphics that plague other TV encoders.
3.6.2.8 Position
There are many TV manufacturers, and most models display the active picture in
a slightly different position relative to the bezel of the television itself. To allow
the end-user the ability to position the TV picture directly in the middle of his
screen, or any other reasonable location, Conexant recommends inclusion of
several Position control buttons.
There should be four directional controls included; two for horizontal
adjustment and two for vertical adjustment. For practical usage, the maximum or
limit adjustment amounts should be 25 pixels horizontally and 10 lines vertically
from the default position. Values greater than these cause a good portion of the
active region to be hidden behind the bezel of the TV thus rendering this area
useless.
From experience, Conexant recommends incrementing the graphics
controller’s HSYNC_START register by 5 pixels every time the LEFT(= ‘–’) or
RIGHT(= ‘+’) button is clicked within the GUI. Every mouse click will also
require reprogramming the CX25870/871’s H_BLANKI register so the active
data does not get chopped off on the opposite side.
Vertically, the software driver should add or subtract two lines from the prior
vertical position every time the UP(= ‘+’) or DOWN(= ‘–’) button is clicked
within the GUI. This means that the VSYNC_START register should be
increased or decreased by two lines for every vertical click by the end-user. The
corresponding modification that needs to be made to the CX25870/871 is an
add/subtract of two lines to the original value in its V_BLANKI register.
As an illustration, assume the end user clicked on the Right button once.
Internally, this action would mean that the graphics controller’s new
HSYNC_START register value needs to be {HSYNC_STARTdefault –5 pixels}.
As the timing master, this would force the controller to issue its HSYNC* digital
signal’s leading edge five pixel clock cycles earlier in time. The software engineer
also must add five pixels to the controller’s HSYNC_END register to maintain the
original HSYNC* pulse duration (8–20 pixels is common). Finally, within the
CX25870/871, the H_BLANKI[9:0] register must be increased by five pixels so
the encoder can accommodate the five extra pixels of blanking to start each line
and still display the original active portion of the line.
3-20
Conexant
100381B
CONEXANT [ CONEXANT SYSTEMS, INC ]
