Cyclone V Device Handbook: Volume 2: Transceivers

ID 683586
Date 10/24/2018
Document Table of Contents Transmitter Polarity Inversion

The positive and negative signals of a serial differential link might accidentally be swapped during board layout. The transmitter polarity inversion feature is provided to correct this situation without requiring a board re-spin or major updates to the logic in the FPGA fabric.

A high value on the tx_invpolarity port inverts the polarity of every bit of the input data word to the serializer in the transmitter datapath. Because inverting the polarity of each bit has the same effect as swapping the positive and negative signals of the differential link, correct data is sent to the receiver. The dynamic tx_invpolarity signal might cause initial disparity errors at the receiver of an 8B/10B encoded link. The downstream system must be able to tolerate these disparity errors.

If the polarity inversion is asserted midway through a serializer word, the word will be corrupted.