There was a question during the 8 February electrical ad hoc call about the polarity sensitivity of the Clause 73 Auto-negotiation for backplane and copper cable assembly (AN73) in Clause 73 of IEEE Std. 802.3-2022.
I would like to note that AN73 as defined in IEEE Std. 802.3-2022 is agnostic to polarity. The auto-negotiation page uses DME (differential Manchester encoding) for the bits. The encoding of data using DME bits in a DME page is given in Figure 73-3:
clock transition positions are denoted by changes in output level (a zero -> one or a one -> zero) and data bits are denoted by a transition at the mid point between the clock transitions.
There is a 49th bit that carries a pseudo-random bit (using the polynomial in Figure 73-2) which is generated once per DME page. This “random” bit will result in the inverting or not inverting of the encoded AN73 page. Additionally, the start of the
AN73 page is denoted by a Manchester violation as shown in Figure 73-5, not a specific logic level on the wire such as the Cl 136.8.11 training frame “Frame Marker”. The receiver of a link partner must be able to decode not inverted and inverted AN73 pages
without intervention.
Therefore, there is no polarity sensitivity of AN73.
-Kent