
Intel
82865G/82865GV GMCH Datasheet
175
Functional Description
Scaling Filter and Control
The scaling filter has three vertical taps and five horizontal taps. Arbitrary scaling (per pixel
granularity) for any video source (YUV422 or YUV420) format is supported.
The overlay logic can scale an input image up to 1600X1200 with no major degradation in the filter
used as long as the maximum frequency limitation is met. Display resolution and refresh rate
combinations, where the dot clock is greater than the maximum frequency, require the overlay to
use pixel replication.
5.4.5
Pipes
The display consists of a single pipe. The pipe can operate in a single-wide or “double-wide” mode
at 2X graphics core clock though, it is effectively limited by its display port (350 MHz maximum).
The primary display plane and the cursor plane provides a “double wide” mode to feed the pipe.
Clock Generator Units (DPLL)
The clock generator units provide a stable frequency for driving display devices. It operates by
converting an input reference frequency into an output frequency. The timing generators take their
input from internal DPLL devices that are programmable to generate pixel clocks in the range of
25–350 MHz. Accuracy for VESA timing modes is required to be within
±
0.5%.
The DPLL can take a reference frequency from the external reference input (e.g., DREFCLK) for
the TV clock input (DVOBC_CLKIN).
5.5
Display Interfaces
The GMCH has three display ports; one analog and two digital. Each port can transmit data
according to one or more protocols. The digital ports are connected to an external device that
converts one protocol to another. Examples of this are TV 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 GMCH has one dedicated display port, the analog port. DVO B and DVO C are multiplexed
with the AGP interface and are not available if an external AGP graphics device is in use. When a
system uses an AGP connector, DVO ports B and C can be used via an ADD (AGP Digital
Display) card. Ports B and C can also operate in dual-channel mode, where the data bus is
connected to both display ports, allowing a single device to take data at twice the pixel rate.
The GMCH’s analog port uses an integrated 350 MHz RAMDAC that can directly drive a standard
progressive scan analog monitor up to a resolution of 2048x1536 pixels with 32-bit color at 75 Hz.
The GMCH’s DVO ports are each capable of driving a 165 MHz pixel clock. Each port is capable
of driving a digital display up to 1600x1200 @ 60Hz. When in dual-channel mode, the GMCH can
drive a flat panel up to 2048x1536 @ 60Hz or dCRT/HDTV up to 1920x1080 @ 85Hz.
The GMCH is compliant with
Digital Visual Interface (DVI) Specification, Revision 1.0
. When
combined with a DVI compliant external device and connector, the GMCH has a high-speed
interface to a digital display (e.g., flat panel or digital CRT).