The STE400P, also referred to as STEPHY4, is a high performance Fast Ethernet physical layer interface for 10BASE-T and 100BASE-TX applications. It was designed with advanced CMOS technology to provide a Media Independent Interface (MII) for easy attachment to 10/100 Media Access Controllers (MAC) and a physical media interface for 100BASETX of IEEE802.3u and 10BASE-T of IEEE802.3. The STE400P supports both half-duplex and full-duplex operation, at 10 and 100 Mbps operation. Its operating mode can be set using auto-negotiation, parallel detection or manual control. It also allows for the support of auto-negotiation functions for speed and duplex detection.