The UC3-C2 Xplained has an RJ45 connector with built-in PHY chip RTL8201and magnetics mounted on the board. The AT32UC3C2512 connects to the physical chip via RMII interface. The RJ45 connector is able to provide the reference clock for the data transmission and it is therefore not necessary to provide this clock. Nevertheless there is also a footprint available that makes it possible to add an oscillator for the reference clock.