The KSZ8081 is a single-supply 10Base-T/100Base-TX Ethernet physical-layer transceiver for transmission and reception of data over standard CAT-5 unshielded twisted pair (UTP) cable. The KSZ8081 is a highly-integrated PHY solution. It reduces board cost and simplifies board layout by using on-chip termination resistors for the differential pairs and by integrating a low-noise regulator to supply the 1.2V core, and by offering 1.8/2.5/3.3V digital I/O interface support. The KSZ8081RNx offers the Reduced Media Independent Interface (RMII) for direct connection to RMII-compliant MACs in Ethernet processors and switches. As the power-up default, the KSZ8081RNA uses a 25MHz crystal to generate all required clocks, including the 50MHz RMII reference clock output for the MAC. The KSZ8081RND is the version that takes in the 50MHz RMII reference clock as the power-up default.