Intel® 500 Series Chipset Family On-Package PCH Datasheet Volume 1

Datasheet

ID 631119
Date 13/07/2021 00:00:00
Public Content
Document Table of Contents

PCI Express* Lane Polarity Inversion

The PCI Express* Base Specification requires polarity inversion to be supported independently by all receivers across a Link—each differential pair within each Lane of a PCIe* Link handles its own polarity inversion. Polarity inversion is applied, as needed, during the initial training sequence of a Lane. In other words, a Lane will still function correctly even if a positive (Tx+) signal from a transmitter is connected to the negative (Rx-) signal of the receiver. Polarity inversion eliminates the need to untangle a trace route to reverse a signal polarity difference within a differential pair and no special configuration settings are necessary in the PCH to enable it.

Note:The polarity inversion does not imply direction inversion or direction reversal; that is, the Tx differential pair from one device must still connect to the Rx differential pair on the receiving device, per the PCIe* Base Specification. Polarity Inversion is not the same as “PCI Express* Controller Lane Reversal”.