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Intel
82865G/82865GV GMCH Datasheet
179
Functional Description
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 accomplished using the external encoders 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 connectors support includes the CVBS, S-Video, Component, and SCART connectors.
The external TV encoder in use will determine the method of support.
5.5.2.1.5
DDC (Display Data Channel)
The multiplexed digital display interface uses the MDVI_CLK and MDVI_DATA signals to
interrogate the panel. The GMCH supports the DDC2B protocol to initiate the transfer of EDID
data. The multiplexed digital display interface uses the M_I
2
C bus to interrogate the external
transmitter. A third set of signals (MDDC_CLK and MDDC_DATA) is available for a variety of
purposes. They can be used as a second DDC pair when two TMDS transmitters are used, or as a
second I
2
C pair if there are multiple devices (e.g., PROM and DVO device) that need I
2
C and there
is a speed or addressing conflict.
The GMCH implements a hardware GMBus controller that can be used to control these signals.
This allows higher speed transactions (up to 400 kHz) on theses lines than was allowed with
previous software centric ‘bit-bashing’ techniques.
5.5.2.1.6
Optional High-Speed (Dual-Channel) Interface
The multiplexed digital display ports can operate in either two 12-bit port modes or one 24-bit
mode. The 24-bit mode uses the 12-bit DVOC data pins combined with the DVOB data pins to
make a 24-bit bus. This doubles the transfer rate capabilities of the port. In the single port case,
horizontal periods have a granularity of a single pixel clock; in the double case, horizontal periods
have a granularity of two pixel clocks. In both cases, data is transferred on both edges of the
differential clock. The GMCH can output the data in a high-low fashion, with the lower 12 bits of
the pixel on DVOC and the upper 12 bits of data on DVOB. In this manner, the GMCH transfers an
entire pixel per clock edge (2 pixels per clock). In addition to this, the GMCH also can transfer
dual-channel data in odd-even format. In this mode, the GMCH transfers all odd pixels on one
DVO, and all even pixels on the other DVO. In this format, each DVO will see both the high and
low half of the pixel, but will only see half of the pixels transferred. As in high-low mode, 2 full
pixels are transferred per clock period. This ordering can be modified through DVO control
registers.