Datasheet

3−1
3 Feature/Protocol Descriptions
The following sections give an overview of the PCI2050B PCI-to-PCI bridge features and functionality. Figure 3−1
shows a simplified block diagram of a typical system implementation using the PCI2050B bridge.
PCI Option Card
CPU
Memory
Host
Bridge
PCI2050B
PCI
Device
PCI
Device
PCI Bus 0
PCI Bus 1
Host Bus
PCI Option Slot
PCI2050B
PCI
Device
PCI
Device
PCI Bus 2
(Option)
PCI Option Card
Figure 3−1. System Block Diagram
3.1 Introduction to the PCI2050B Bridge
The PCI2050B device is a bridge between two PCI buses and is compliant with both the PCI Local Bus Specification
and the PCI-to-PCI Bridge Specification. The bridge supports two 32-bit PCI buses operating at a maximum of
66 MHz. The primary and secondary buses operate independently in either 3.3-V or 5-V signaling environment. The
core logic of the bridge, however, is powered at 3.3 V to reduce power consumption.
For PCI2050B, the FIFO size is 32 DW for delayed responses (3 each direction) 64 DW posted write and delayed
request FIFO (1 each direction).
Host software interacts with the bridge through internal registers. These internal registers provide the standard PCI
status and control for both the primary and secondary buses. Many vendor-specific features that exist in the TI
extension register set are included in the bridge. The PCI configuration header of the bridge is only accessible from
the primary PCI interface.
The bridge provides internal arbitration for the nine possible secondary bus masters, and provides each with a
dedicated active low request/grant pair (REQ
/GNT). The arbiter features a two-tier rotational scheme with the
PCI2050B bridge defaulting to the highest priority tier. The PCI2050B device also supports external arbitration.
Upon system power up, power-on self-test (POST) software configures the bridge according to the devices that exist
on subordinate buses, and enables performance-enhancing features of the PCI2050B bridge. In a typical system,
this is the only communication with the bridge internal register set.