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AMD Geode™ SC1200/SC1201 Processor Data Book 313
Video Processor Module
32579B
7.2 Functional Description
To understand why the Video Processor functions as it
does, it is first important to understand the difference
between video and graphics. Video is pictures in motion,
which usually starts out in an encoded format (i.e.,
MPEG2, AVI, MPEG4) or is a TV broadcast. These pic-
tures or frames are generally dynamic and are drawn 24 to
30 frames per second. Conversely, graphic data is rela-
tively static and is drawn - usually using hardware accelera-
tors. Most IA devices need to support both video and
graphics displayed at the same time. For some IA devices,
such as set-top boxes, video is dominant. While for other
devices, such as consumer access devices and thin clients,
graphics is dominant. What this means for the Video Pro-
cessor is that for video centric devices, graphics overlays
the video; and for graphics centric devices, video overlays
the graphics.
Video centric devices usually render video full frame. On a
TV, the video image is larger than the screen and will actu-
ally spill outside or overscan the TV’s viewable area by
about 10%. This is done intentionally to eliminate any black
border. Consequently graphic overlays, such as menus and
control buttons, must account for overscan when displaying
on a TV. Conversely, when the output device is a CRT mon-
itor or a TFT panel there is no overscan so the graphic
overlays do not have to deal with this issue. Common soft-
ware drivers can easily support either type of display
device.
Graphic centric devices render graphics full frame. Again, if
the TV is the output device, overscan comes into play, but
the graphic content cannot be allowed into the overscan
area. Software drivers and/or applications must take that
into account. The video overlay, when it is active, is usually
rendered less than full frame. For some IA devices the
video and graphics exchange dominance is application-
dependent. An example of this is an Internet enabled set-
top box where video is dominant during TV viewing and
graphics is dominant during Web browsing.
Video Support
The SC1200/SC1201 processor gets video from two
sources, either the VIP block or the GX1 module’s video
frame buffer. The VIP block supports the CCIR-656 data
protocol. The CCIR-656 protocol supports TV data (NTSC
or PAL) and defines the format for active video data and
vertical blanking interval (VBI) data. Conforming CCIR-656
data matches exactly what is needed for a TV: full frame,
interlaced, 27 MHz pixel clock, and 50 or 60 Hz refresh
rate. Full frame pixel resolution and the refresh rate
depends on the TV standard: NTSC, PAL, or SECAM.
If the VIP input data is full frame (conforming data) and the
output is the TV interface, then the data can go directly
from the VIP block to the Video Formatter. This is known as
Direct Video mode. In this mode, the data never leaves the
Video Processor module. If the output is to a CRT or TFT
interface, or the VIP data is less than full frame (non con-
forming data), the VIP block will bus master the video data
to the GX1 module’s Video Frame Buffer. The GX1 mod-
ule’s Display Controller then moves the video data out of
the Video Frame Buffer and sends it to the Video Format-
ter. Using this method the temporal (refresh rate) and/or
spatial (image less then full screen) differences between
the VIP data and the output device are reconciled. This
method is known as Capture Video mode. How each mode
is setup and operates is explained further in Section 7.2.1
on page 315.
VBI Support
VBI (vertical blanking interval) data is placed in the video
data stream during a portion of the vertical retrace period.
The vertical retrace period physically consists of several
horizontal lines (24 for NTSC and 25 for PAL systems) of
non-active video. Data can be placed on some of these
lines for other uses.
The active video and vertical retrace period horizontal lines
are logically defined into 23 types: logical line 2 through
logical line 24 (no logical line 1). Logical lines 2 through 23
occur during the vertical retrace period and logical line 24
represents all the active video lines. Logical lines 10
through 21 for NTSC and 6 through 23 for PAL are the
nominal VBI lines. The rest of the logical lines, 2 through 9,
22, and 23 for NTSC and 2 through 6 for PAL occur during
the vertical retrace period but do not normally carry user
data. An example of VBI usage is Closed Captioning,
which occupies VBI logical line 21 for NTSC. Figure 7-2
and Figure 7-3 on page 314 show the (relationship
between the) physical scan lines and logical scan lines for
the odd and even fields in the NTSC format.