82845G Datasheet, PDF (133/193 Pages) Intel Corporation – Intel 82845G/82845GL/82845GV Graphics and Memory Controller Hub (GMCH)

Functional Description
4.5.2
4.5.2.1
DDC (Display Data Channel)
DDC is a standard defined by VESA. Its purpose is to allow communication between the host
system and display. Both configuration and control information can be exchanged allowing plug-
and-play systems to be realized. Support for DDC 1 and 2 is implemented. The GMCH uses the
DDCA_Clk and Data to communicate with the analog monitor.
Digital Display Interface
The GMCH has several options for driving digital displays. The GMCH contains two DVO ports
that are multiplexed on the AGP interface. When an external AGP graphics accelerator is not
present, the GMCH can use the multiplexed DVO ports to provide extra digital display options.
These additional digital display capabilities may be provided through an ADD card, which is
designed to plug in to a 1.5 V AGP connector.
Digital Display Channels – DVOB and DVOC
The shared DVO ports each support a pixel clock up to 165 MHz and can support a variety of
transmission devices. When using a 24-bit external transmitter, it will be possible to pair the two
DVO ports in dual-channel mode to support a single digital display with higher resolutions and
refresh rates. In this mode, the GMCH is capable of driving pixel clock up to 330 MHz.
The GMCH multiplexes an ADD_DETECT signal with the GPAR signal on the AGP bus. This
signal acts as a strap and indicates whether the interface is in AGP or DVO mode. The GMCH has
an internal pull-up on this signal that pulls it high. If an ADD card is present, the signal is pulled
low on the ADD card and the GMCH operates in DVO mode. Motherboards that do not use an
AGP connector should have a pull-down resistor on ADD_DETECT if digital display devices are
connected to the AGP/DVO interface.
ADD Card
When an 845G chipset utilizes an AGP connector, the multiplexed DVO ports can be used via an
ADD card. The ADD card fits in a 1.5 V AGP connector.
TMDS Capabilities
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). When combining the two multiplexed
DVO ports, the GMCH can drive a flat panel up to 2048x1536 at 60 Hz or a dCRT/HDTV up to
1920x1080 at 85 Hz. Flat Panel is a fixed resolution display. While the GMCH has no native panel
fitting capabilities, it supports panel fitting in the transmitter, receiver, or an external device. The
GMCH, however, provides unscaled mode where the display is centered on the panel.
LVDS Capabilities
The GMCH can use the multiplexed DVO ports to drive an LVDS transmitter. A Flat Panel is a
fixed resolution display. While the GMCH has no native panel fitting capabilities, it supports panel
fitting in the transmitter, receiver, or an external device. The GMCH provides unscaled mode
where the display is centered on the panel. The GMCH supports scaling in the LVDS transmitter
through the DVOB (or DVOC)_STL pin, multiplexed with DVOB (or DVOC)_FLD.
Intel^® 82845G/82845GL/82845GV GMCH Datasheet
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