Jasper Lake EDS Vol1
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. It is important to note that 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”.