82845G Datasheet, PDF (105/193 Pages) Intel Corporation – Intel 82845G/82845GL/82845GV Graphics and Memory Controller Hub (GMCH)

Functional Description
Functional Description
4
This chapter describes the GMCH interfaces and functional units including the processor system
bus interface, the AGP interface, system memory controller, integrated graphics device, DVO
interfaces, display interfaces, power management, and clocking.
4.1
Processor System Bus
The GMCH supports a single mPGA 478 processor with PSB frequencies of 400 MHz (100 MHz
HCLK) / 533 MHz (133 MHz HCLK) and it also supports Hyper-Threading Technology. The
GMCH uses a scalable PSB VTT between 1.15 V and 1.75 V and on-die termination. The GMCH
supports 32-bit host addressing (decoding up to 4 GB of the processor’s memory address space).
Host-initiated I/O cycles are decoded to the AGP/PCI_B, hub interface or GMCH configuration
space. Host-initiated memory cycles are decoded to AGP/PCI_B, the hub interface, or system
memory. All memory accesses from the host interface that hit the graphics aperture are translated
using an AGP address translation table. AGP/PCI_B device accesses to non-cacheable system
memory are not snooped on the host bus. Memory accesses initiated from AGP/PCI_B using PCI
semantics and from the hub interface to system memory are snooped on the host bus.
The GMCH supports the Pentium 4 processor subset of the Enhanced Mode Scaleable Bus. The
cache line size is 64 bytes. Source synchronous transfer is used for the address and data signals. At
100/133 MHz bus clock the address signals are double pumped to run at 200/266 MHz and a new
address can be generated every other bus clock. At 100/133 MHz bus clock the data signals are
quad pumped to run at 400/533 MHz and an entire 64-B cache line can be transferred in two bus
clocks.
The GMCH integrates AGTL+ termination resistors on die. The GMCH has an IOQ depth of 8.
The GMCH supports one outstanding Deferred transaction on the PSB.
4.1.1 PSB Dynamic Bus Inversion
The GMCH supports Dynamic Bus Inversion (DBI) when driving, and when receiving data from
the system bus. DBI limits the number of data signals that are driven to a low voltage on each quad
pumped data phase. This decreases the power consumption of the GMCH. DINV_[3:0]# indicate if
the corresponding 16 bits of data are inverted on the bus for each quad pumped data phase
(see Table 4-1).
Table 4-1. DINV Signals vs. Data Bytes
DINV[3:0]#
DINV_0#
DINV_1#
DINV_2#
DINV_3#
Data Bits
HD_[15:0]#
HD_[31:16]#
HD_[47:32]#
HD_[63:48]#
Intel^® 82845G/82845GL/82845GV GMCH Datasheet
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