82845G Datasheet, PDF (134/193 Pages) Intel Corporation – Intel 82845G/82845GL/82845GV Graphics and Memory Controller Hub (GMCH)

Functional Description
TV-Out Capabilities
While traditional TVs are not digital displays, the GMCH uses a digital display channel to
communicate with a TV-Out transmitter. For that reason, the GMCH considers a TV-Output to be a
digital display. The GMCH supports NTSC/PAL/SECAM standard definition formats. The GMCH
generates the proper timing for the external encoder. The external encoder is responsible for
generation of the proper format signal. Since the multiplexed DVO interface is 1.5 V, care should
be taken to ensure that the TV encoder is operational at that signaling voltage.
A NTSC/PAL/SECAM display on the TV-Out port can be configured to be the boot device. It is
necessary to ensure that appropriate BIOS support is provided.
The TV-Out interface on the GMCH is addressable as a master device. This allows an external TV
encoder device to drive a pixel clock signal on DVOBC_CLKINT# that the GMCH uses as a
reference frequency. The frequency of this clock is dependent on the output resolution required.
Data is driven to the encoder across 12 data lines, along with a clock pair and sync signals. The
encoder can expect a continuous flow of data from the GMCH because data will not be throttled.
Flicker Filter and Overscan Compensation
The overscan compensation scaling and the flicker filter is done in the external TV encoder chip.
Care must be taken to allow for support of TV sets with high performance de-interlacers and
progressive scan displays connected to by way of a non-interlaced signal. Timing is generated with
pixel granularity to allow more overscan ratios to be supported.
Direct YUV from Overlay
When source material is in the YUV format and is destined for a device that can take YUV format
data in, it is desired to send the data without converting it to RGB. This avoids the truncation errors
associated with multiple color conversion steps. The common situation is that the overlay source
data is in the YUV format and bypasses the conversion to RBG as it is sent to the TV port directly.
Sync Lock Support
Sync lock to the TV is done using the external encoder’s PLL combined with the display phase
detector mechanism. The availability of this feature is determined by which external encoder is in
use.
Analog Content Protection
Analog content protection is provided through the external encoder using Macrovision 7.01. DVD
software must verify the presence of a Macrovision TV encoder before playback continues. Simple
attempts to disable the Macrovision operation must be detected.
Connectors
Target TV connector support includes the CVBS, S-Video, Component, and SCART connectors.
The external TV encoder in use determines the method of support.
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Intel^® 82845G/82845GL/82845GV GMCH Datasheet