1.0 Functional Description
CX25870/871
1.3 Device Description
Flicker-Free Video Encoder with Ultrascale Technology
Figure 1-4 illustrates higher resolutions (i.e., 800x600 or greater), for some
data master devices that require more Horizontal Blanking Time than the
CX25870/871 provides in standard clocking mode, for dual display of certain
overscan compensation percentage pairs. For example, a graphics controller may
require a minimum total of 1.25 µs of Horizontal Blanking time per line while
clocking a frame with an active resolution of 800x600 to the encoder. If this were
the case, the entire set of overscan compensation solutions charted at the 1 µs
diagonal plot line (denoted with a dot-dash-dot) and below are made unavailable
to the designer. The result is a more limited set of overscan pairs to choose from,
and correspondingly less size control for the picture when displayed on a
television.
Figure 1-4. Allowable Overscan Compensation Ratios for Dual Display, 800x600 Input/NTSC Output
Overscan Compensation Percentage Pairs for 800x600 NTSC
24
3 µs
22
20
2 µs
18
16
1 µs
14
.75 µs
12
0 µs Horizontal Blanking
10
8
8
10
12
14
16
18
20
22
Vertical Overscan Compensation Percentage
Legend:
= Pixel Clock Solution
= 8-Cycle Character Clock Solution
= 9-Cycle Character Clock Solution
NOTE(S):
Use this chart for PAL M and PAL 60 allowable overscan ratios
1-16
Conexant
100381B
CONEXANT [ CONEXANT SYSTEMS, INC ]
