W9970CF Datasheet, PDF (4/6 Pages) Winbond – VIDEO GRAPHICS CONTROLLER

W9970CF
GRAPHICS ENGINE
The 64-bit graphics engine (GE) is specially designed
to improve the performance of applications such as
Microsoft Windows and other graphical user interface
software. Performance is enhanced by accelerating
GUI functions such as BitBLTs, Bresenham line draw,
and short stroke vector. The GE performs several types
of BitBLTs, including HostBLT, pattern BLT,
color/font expanding BLT, transparent BLT, color
expansion, and rectangle fill, with 256 ROPS on
source, pattern, and destination. The graphics engine
operates at all pixel depths in enhanced modes,
including 8/16/24 bit-per-pixel modes. A 64 × 64 × 2
or 32 × 32 × 2 hardware cursor, fully compatible with
Microsoft Windows, is used to speed up cursor
performance and accelerate all graphics operations by
eliminating the CPU overhead associated with cursor
manipulation.
VIDEO ACCELERATOR
The Video Accelerator is a high-quality video
processor for enhancing and displaying video images.
It not only accelerates software video playback but also
facilitates the interface to MPEG-1 video decoders and
TV decoders.
The video accelerator employs back-end color space
conversion and a scaling mechanism (see Figure 3).
Video and game-generated graphics frames are read
from an off-screen buffer and sent to the overlay and
blending control block as the secondary stream. Color
space conversion and scaling are performed along the
way. This on-the-fly video acceleration and overlaying
ensure game and video playback at full speed.
Color Space Conversion
The built-in color space converter converts YUV
format to 24-bit RGB format according to the CCIR
601-2 Recommendation.
Down Scaling
The down-scaling function is performed by dropping
pixels or lines. To support arbitrary scaling factors, the
video accelerator uses a digital differential
accumulator (DDA) to drop pixels or lines smoothly.
The scaling factor may range from 1/64 to 63/64.
Scaling up by 2D Interpolation
Rather than duplicating pixels or lines for
enlargement, the video accelerator uses a 2-D bilinear
interpolation algorithm to enhance the output for
high-quality video display.
The interpolation algorithm creates seven weighted,
intermediate values between two original pixels or
lines, which allows a maximum of 800% enlargement.
For non-integer scaling, a 10-bit DDA with 1/1024
resolution is used to interpolate pixels by averaging.
2x Scaling
The 2x scaling located in the RAMDAC is used to
optionally scale up, both horizontally and vertically, by
a factor of 2 for the overlaid data stream. This is used to
scale 320 × 240 game-generated frames to full screen.
Filtering
The video accelerator provides horizontal RGB or
YUV filtering to reduce noise and aliasing artifacts in
the video data stream
Cropping
A rectangular cropping window is supported in the
video accelerator for subsampling the incoming video
data stream. Only video located in the cropping
window can be stored into the off-screen buffer.
Alpha Blending
Alpha blending is supported for overlaying the
primary stream and secondary stream. The alpha value
can be 1 bit or 3 bits. The 1-bit alpha depth overlaying
(also known as software key) is supported only for the
pixel format of RGB 1:5:5:5, where the alpha bit value
of 0 is transparent and value of 1 is opaque.
An overlay control register specifies the 3-bit alpha
value for the primary stream (Kp) and secondary
stream (Ks). Note that Kp + Ks must be ≤ 8. The
blending equation is [Pp × Kp + Ps × Ks]/8, where Pp
Preliminary
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March 1996