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.