The MAC I/F is only functional when the DCMAC Subsystem is configured in Independent MAC and PCS+FEC mode and the AXI interface is correspondingly in Channelized Segmented AXI4-Stream mode. The transmit and receive MAC I/F ports provide line-side connections to the DCMAC Subsystem's internal time-sliced MAC. In terms of data content, the interfaces move 66b Ethernet blocks out of the transmit MAC and into the receive MAC.