cx25870 Conexant Systems, Inc., cx25870 Datasheet - Page 33

• Manufacturer Part Number: cx25870
• Description: Video Encoder With Adaptive Flicker Filtering And Hdtv Output
• Manufacturer: Conexant Systems, Inc.

CX25870/871
Flicker-Free Video Encoder with Ultrascale Technology
Table 1-6. Autoconfiguration Solutions that Utilize 3:2 Clocking Mode
100381B
Autoconfiguration
Mode #
10
11
14
15
18
22
26
30
34
40
42
43
1024x768
1024x768
1024x768
1024x768
800x600
800x600
1024x768
1024x768
800x600
800x600
1024x768
1024x768
Active Resolution
does not face this constraint any longer. By choosing an appropriate
autoconfiguration mode, setting the PLL_32CLK bit to 1, and altering the values
for various timing registers within the controller and encoder (e.g.,
H_CLKI = HTOTAL, VLINES_I = VTOTAL, H_BLANKI, V_BLANKI, etc.),
the encoder switches into the 3:2 Clock mode. While in this operational state,
additional solutions in the overscan-compensation-pairs domain for higher
resolutions now exist. In addition, the encoder now allows the data master (e.g.,
graphics controller) to send digital data to it at a faster rate than is clocked out of
the encoder. Specifically, the CX25870/871 begins to transfer pixels out at a rate
of [2/3] that of the CLKI input frequency. In other words, the pixel input
frequency clocks in data at a ratio of [3:2] or 1½ times faster than the
CX25870/871 outputs the analog pixel data. In this mode, the encoder's expansive
on-chip FIFO bridges the frequency difference that now exists between the
digital-timing input and mixed-signal encoder output blocks of the CX25870/871.
The result is a much closer match in the available overscan percentages in the
horizontal and vertical direction for the higher resolutions. This ensures the TV
Out picture appears more orthogonal where the amount of blanking is nearly
equal on all sides of the image.
resolutions, the user should use a 3:2 Clocking Mode only when necessary at
800x600, and always at 1024x768. For software programming ease, some of the
autoconfiguration modes for 800x600 and all for the 1024x768 resolution are 3:2
solutions already. The specific modes that use the 3:2 clock feature are contained
in
Appendix C
Since the CX25870/871 contains this new 3:2 Clocking Mode, the designer
Since the Horizontal Blanking Time only becomes a critical issue at higher
and summarized in
Type of Digital Input
RGB
RGB
YCrCb
YCrCb
RGB
YCrCb
RGB
YCrCb
RGB
RGB
RGB
RGB
Conexant
Table 1-6
Standard
Standard
Standard
Standard
Lower
Lower
Lower
Lower
Higher
Alternate
Higher
Higher
Overscan Ratio
below.
1.0 Functional Description
NTSC
PAL-BDGHI
NTSC
PAL-BDGHI
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
PAL-BDGHI
1.3 Device Description
Video Output Type
1-17