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PCI Configuration Space
archically behind it. If the bus number of the configuration cycle matches the bus num-
ber of the bridge chip's secondary PCI interface, it will accept the configuration cycle,
decode it, and generate a PCI configuration cycle with ad<1:0> = 00 on its secondary
PCI interface. If the bus number is within the range of bus numbers that may exist
hierarchically behind its secondary PCI interface, the bridge chip passes the PCI con-
figuration cycle on unmodified (ad<1:0> = 01). It will be accepted by a bridge further
downstream. Figure 1–16 shows a typical PCI hierarchy. This is only one example of
how the 21174 can be used in a system design.
Figure 1–16 PCI Bus Hierarchy
Bcache
21164
PCI-to-(E)ISA
Bridge
(E)ISA
Bus
System Address Space
A–30
Memory
21174
ASIC
64-Bit PCI Bus
PCI-to-PCI
Bridge
32-Bit
Slots
Slot
Slot
Slot
Audio
64-Bit Slots
PCI
Graphics
Internal PCI
SCSI
SCSI
SCSI
Ethernet
LJ-05401.AI4
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