82845PE Datasheet, PDF (18/176 Pages) Intel Corporation – 82845GE Graphics and Memory Controller Hub (GMCH) and 82845PE Memory Controller Hub (MCH)

Introduction
1.4.4
1.4.5
Multiplexed AGP and Intel^® DVO Port Interface
The 82845GE GMCH multiplexes an AGP interface with two DVO ports. When an external AGP
device is installed in the system, the IGD functionality is disabled.
AGP Interface (Intel^® 82845GE and 82845PE)
A single AGP or PCI-66 component or connector (not both) is supported by the (G)MCH’s AGP
interface. Support for a single PCI-66 device is limited to the subset supported by the Accelerated
Graphics Port Interface Specification, Revision 2.0. The AGP/PCI_B buffers operate only in 1.5 V
mode and support the AGP 1.5 V Connector.
For the 82845GE, an external graphics accelerator is not a requirement due to the GMCH’s
integrated graphics capabilities. The BIOS will disable the IGD if an external AGP device is
detected.
The AGP/PCI_B interface supports up to 4X AGP signaling and up to 4X Fast Writes. AGP
semantic cycles to system memory are not snooped on the host bus. PCI semantic cycles to system
memory are snooped on the host bus. The (G)MCH supports PIPE# or SBA_[7:0] AGP address
mechanisms, but not both simultaneously. Either the PIPE# or the SBA_[7:0] mechanism must be
selected during system initialization. The (G)MCH contains a 32-deep AGP request queue. High
priority accesses are supported.
Multiplexed Intel^® DVO Port Interface (Intel^® 82845GE only)
The 82845GE GMCH supports two multiplexed DVO ports that each drive pixel clocks up to
165 MHz. When an AGP connector is present, the GMCH can make use of these digital display
channels via an AGP Digital Display card.
Graphics Overview (Intel^® 82845GE only)
The 82845GE GMCH provides an integrated graphics accelerator delivering 3D, 2D and video
capabilities. The GMCH contains an extensive set of instructions for 3D operations, BLT and
Stretch BLT operations, motion compensation, overlay, and display control. The GMCH’s video
engines support video conferencing and other video applications. The GMCH does not support a
dedicated local graphics memory interface, it can only be used in a UMA configuration. In
addition, the GMCH supports external graphics accelerators via AGP, but cannot work
concurrently with an external AGP graphics device.
High bandwidth access to data is provided through the system memory port. The GMCH can
access graphics data located in system memory at 2.2 GB/s (DDR266) or 2.7 GB/s (DDR333). The
GMCH uses Intel’s Direct Memory Execution model to fetch textures from system memory. The
GMCH includes a cache controller to avoid frequent memory fetches of recently used texture data.
The GMCH also provides 2D hardware acceleration for block-level transfers of data (BLTs). The
BLT engine provides the ability to copy a source block of data to a destination and perform raster
operations on the data using a pattern, and/or another destination. Performing these common tasks
in hardware reduces processor load; thus, improving performance. The internal graphics device
must be disabled when an attached AGP device is used.
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Intel^® 82845GE/82845PE Datasheet