RG82855GMESL72L Datasheet, PDF (153/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

Functional Description
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6.4.8.2
6.4.8.3
6.5
6.5.1
Hardware Motion Compensation
The HWMC process consists of reconstructing a new picture by predicting (either forward,
backward, or bi-directional) the resulting pixel colors from one or more reference pictures. The
GMCH receives the video stream and implements Motion Compensation and subsequent steps in
hardware. Performing Motion Compensation in hardware reduces the processor demand of
software-based MPEG-2 decoding, and thus improves system performance.
Sub-picture Support
Sub-picture is used for two purposes: Subtitles for movie captions, which are superimposed on a
main picture, and for menus to provide some visual operation environments for the user.
DVD allows movie subtitles to be recorded as sub-pictures. On a DVD disc, it is called subtitle
because it has been prepared for storing captions. Since the disc can have a maximum of 32 tracks
for subtitles, they can be used for various applications, for example, as Subtitles in different
languages.
There are two kinds of menus, the System menus and other In-Title menus. First, the System
menus are displayed and operated at startup of or during the playback of the disc or from the stop
state. Second, In-Title menus can be programmed as a combination of Sub-picture and Highlight
commands to be displayed during playback of the disc.
The GMCH supports sub-picture for DVD by mixing the two video streams via alpha blending.
Unlike color keying, alpha blending provides a softer effect and each pixel that is displayed is a
composite between the two video stream pixels. The GMCH can utilize four methods when
dealing with sub-pictures. This flexibility means that the GMCH can work with all sub-picture
formats.
Display Interface
The GMCH has four dedicated display ports: an Analog CRT port, the Internal LVDS interface,
and two Digital display ports, DVOB and C. DVOB and C can support TV-out encoders, external
DACs, LVDS transmitters, and TMDS transmitters. Each display port has control signals that
may be used to control, configure and/or determine the capabilities of an external device. The data
that is sent out the display ports are selected from one of the two possible sources, display pipe A
or display pipe B, except for the LVDS port which can only be driven on Pipe B.
The GMCH’s digital display port is capable of driving a 165 MHz pixel clock on a single DVO
port, or 330 MHz pixel clock by combining DVOB and DVOC.
Analog Display Port Characteristics
The Analog display port provides an RGB signal output along with an HSYNC and VSYNC
signal. There is an associated DDC signal pair that is implemented using GPIO pins dedicated to
the analog port. The intended target device is for a CRT based monitor with a VGA connector.
Datasheet
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