21154 PCI-to-PCI Bridge
Datasheet
Product Features
■ Complies fully with the PCI Local Bus
Specification, Revision 2.1
■ Provides a 4-pin general-purpose I/O
interface, accessible through device-
specific configuration space
■ Provides enhanced address decoding:
—A 32-bit I/O address range
■ Complies fully with the PCI Power
Management Specification, Revision 1.01
■ Supports 64-bit extension signals on the
primary and secondary interfaces
—A 32-bit memory-mapped I/O address
range
■ Implements delayed transactions for all PCI
configuration, I/O, and memory read
commands–up to three transactions
simultaneously in each direction
—A 64-bit prefetchable memory address
range
—ISA-aware mode for legacy support in
the first 64KB of I/O address range
■
Allows 152 bytes of buffering (data and
address) for upstream posted memory write
commands and 88 bytes of buffering for
downstream posted memory write
commands—up to nine upstream and five
downstream posted write transactions
simultaneously
— VGA addressing and VGA palette
snooping support
■ Includes live insertion support
■ Supports PCI transaction forwarding for the
following commands:
■ Allows 152 bytes of read data buffering
upstream and 152 bytes of read data
buffering downstream
—All I/O and memory commands
—Type 1 to Type 1 configuration
commands
■ Provides concurrent primary and secondary
bus operation to isolate traffic
—Type 1 to Type 0 configuration
commands (downstream only)
■ Provides ten secondary clock outputs:
—Low skew, permitting direct drive of
option slots
—All Type 1 to special cycle configuration
commands
—Individual clock disables, capable of
automatic configuration during reset
■ Includes downstream lock support
■ Supports both 5-V and 3.3-V signaling
■ Provides arbitration support for nine
environments
secondary bus devices:
—A programmable 2-level arbiter
■ Available in both 33 MHz and 66 Mhz
versions
—Hardware disable control, permitting use
of an external arbiter
■ Provides an IEEE standard 1149.1 JTAG
interface
1. For the 21154–AB and later revisions only. The 21154–AA does not implement this feature.
Order Number: 278108-002
July 1999