Functional Description; Host Interface; Fsb Gtl+ Termination; Fsb Dynamic Bus Inversion - Intel 925 - Pentium D 925 3.0GHz 800MHz 4MB-Cache Socket 775 CPU Datasheet

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Functional Description

This chapter describes the MCH interfaces and major functional units.
10.1

Host Interface

The MCH 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.
The address signals are double pumped, and a new address can be generated every other bus
clock. When the 82925X MCH bus clock runs at 200 MHz, the address signals run at 400 MT/s
for a maximum address queue rate of 66/100 million addresses/sec. The data is quad pumped and
an entire 64 byte cache line can be transferred in two bus clocks. With a bus clock of 200 MHz,
the data signals run at 800 MT/s for a maximum bandwidth of 6.4 GB/s. When the 82925XE
MCH bus clock runs at 266 MHz, the address signals run at 533 MT/s for a maximum queue rate
of 88/133 million addresses/sec. With a 82925XE bus clock at 266 MHz, the data signals run at
1066 MT/s for a maximum bandwidth of 8.5 GB/s.
The FSB interface supports up to 12 simultaneous outstanding transactions. The MCH supports
only one outstanding deferred transaction on the FSB.
10.1.1

FSB GTL+ Termination

The MCH integrates GTL+ termination resistors on die. Also, approximately
2.8 pf (fast) – 3.3 pf (slow) per pad of on die capacitance will be implemented to provide better
FSB electrical performance.
10.1.2

FSB Dynamic Bus Inversion

The MCH supports Dynamic Bus Inversion (DBI) when driving and when receiving data from the
processor. DBI limits the number of data signals that are driven to a low voltage on each quad
pumped data phase. This decreases the worst-case power consumption of the MCH.
HDINV[3:0]# indicate if the corresponding 16 bits of data are inverted on the bus for each quad
pumped data phase:
HDINV[3:0]#
HDINV0#
HDINV1#
HDINV2#
HDINV3#
When the processor or the MCH drives data, each 16-bit segment is analyzed. If more than 8 of
the 16 signals would normally be driven low on the bus, the corresponding HDINV# signal will
be asserted and the data will be inverted prior to being driven on the bus. When the processor or
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Intel 82925X/82925XE MCH Datasheet
Data Bits
HD[15:0]#
HD[31:16]#
HD[47:32]#
HD[63:48]#
Functional Description
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