845GL datasheet(134/193 Pages) INTEL

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Functional Description

134

Intel® 82845G/82845GL/82845GV GMCH Datasheet

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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