21555AA/BA and 21555AB/BB Differences

Application Note

5

1.0

Introduction

This document defines the differences between the 21555AA/BA bridge when compared with the

21555AB/BB bridge. The 21555 bridge is a second generation Non-Transparent PCI-to-PCI

bridge.

1.1

Changes to the 21555 Bridge

After the introduction of the 21555AA/BA bridge, two errata were discovered

Additionally, the PCI standards committee ratified the new PCI 2.3 Specification, which required

an additional bit to be added to the control register and status register.

The new 21555AB/BB bridge version addresses all three of these issues.

Note:

This Differences document is not a stand-alone document and does not provide complete 21555

bridge details. The intent here is only to highlight the feature differences between the

21555AA/BA and the 21555BA/BB steppings. Please be sure to review the data sheet and spec

updates for more complete information on the device.

2.0

Stepping Differences

Table 1.

Stepping Differences

3.0

I2O Asynchronous Operation

The 21555AA/BA devices would not operate asynchronously. This behavior has been corrected in

Package Markings

REV_ID

Register

a.

Identified in a PCI system by reading the value in the REV_ID register.

Speed (MHz)

Stepping

Intel FW21555AA

02h

33

A2

Intel FW21555BA

02h

66

A2

Intel FW21555AB

03h

33

A3

Intel FW21555BB

03h

66

A3