CX25870/871
3.0 PC Board Considerations
Flicker-Free Video Encoder with Ultrascale Technology
3.6 Applications Information
Customers are urged to enable the autoconfiguration mode that is in the
middle of each chart as the default Size for each active resolution. To accomplish
this, the encoder’s CONFIG[5:0] bit field must be programmed to the desired
mode. In addition, the graphics controller’s HTOTAL register must be
programmed to match the CX25870/871’s H_CLKI[10:0] value, and VTOTAL
register must be programmed to match the CX25870/871’s V_LINESI[10:0]
value. Other minor modifications may be necessary. The specific procedure to
follow to enable different overscan ratios is explained in an application note titled
Supporting TV Out with Non-Standard Graphics Input Resolutions. Request this
document from your local Conexant Sales representative for help on the Size
video adjustment.
A simpler alternative to independent horizontal and vertical size buttons is to
replace the directional control pad with a slider. This slider would only have 3 tick
marks and would cycle through the different sizes available based on the
autoconfiguration modes that exist for the specific desktop resolution and video
output type. This concept is illustrated in Figure 3-13.
Figure 3-13. Direction-less Size Control Pad
The slider would alter the horizontal and vertical size of the TV picture
simultaneously by changing the overscan percentages by the same amount. Size
control should only be effective for desktop resolutions such as 640x480,
800x600, and 1024x768. Nonstandard resolutions should choose a single size
with a moderate amount of overscan compensation (HOC/VOC = 11 percent–16
percent) and not allow the end-user to deviate from this choice by graying out the
Size slider.
100381B
Conexant
3-25
CONEXANT [ CONEXANT SYSTEMS, INC ]
