2.5.1
Fast Switches for SCART and Digital Overlay
The TVP5146 decoder supports the SCART interface used in European audio/video end equipment to carry
composite video, S-video, and RGB video on the same cable. In the event that composite video and RGB video are
present simultaneously on the video pins assigned to a SCART interface, the TVP5146 decoder assumes they are
pixel synchronous to each other. The timing for both composite video and RGB video is obtained from the composite
source and its derived clock is used to sample RGB video as well. The fast-switch input terminal allows switching
between these two input video sources on a pixel-by-pixel basis. This feature can be used to overlay RGB graphics
for on-screen display onto decoded CVBS video. The fast-switch is a hard-switch; there is no alpha blending between
both sources.
If overlay output is digital supporting eight colors of data, then the TVP5146 decoder can take digital overlay inputs
using terminals C6, C7, and C8. For this mode, the output must be in the 10-bit ITU-R BT.656 mode. Figure 2−20
shows the block diagram of two fast-switches and four delay controls. Overlay delay control is used to adjust timing
between digital RGB and component inputs after the fixed delay (maximum delay of AFE and 2x decimation filter)
is applied. FSO delay control compensates the digital overlay internal delay to match between the FSO and overlay
signals. FSS delay control is synchronized to the SCART signal. The SCART delay control compensates composite
internal path overall delays to match between the CVBS and SCART signals. Table 2−3 shows possible supported
combinations of fast-switch modes.
CVBS
Digital
Overlay RGB
Overlay
Delay
YCbCr
Color
Space
Conversion
SCART
Delay
SCART RGB
FSO
FSO
Delay
FSS
FSS
Delay
Figure 2−20. Fast-Switches for SCART and Digital Overlay
Table 2−3. SCART and Digital Overlay Fast-Switch Modes
MODE
000
001
010
011
100
101
110
111
CVBS
$
SCART
CVBS/S-video
$
digital overlay
Component
$
digital overlay
(CVBS
$
SCART)
$
digital overlay
(CVBS
$
digital overlay)
$
SCART
CVBS
$
(SCART
$
digital overlay)
Composite only
Component only
DESCRIPTION
2−12
TI [ TEXAS INSTRUMENTS ]
