The AX88772A/AX88172A features a USB interface to communicate with a USB Host Controller and is compliant with USB specification V1.1 and V2.0. The AX88772A/AX88172A implements 10/100Mbps Ethernet LAN function based on IEEE802.3, and IEEE802.3u standards with 24KB of embedded SRAM for packet buffering. The AX88772A/AX88172A integrates an on-chip 10/100Mbps Ethernet PHY to simplify system design. The AX88172A provides an optional External Media Interface (EMI) for external PHY or external MAC for different application purposes. The EMI can be a media-independent interface (MII) for implementing 100BASE-FX Ethernet or HomePNA functions. The EMI can also be a Reverse-MII or Reverse Reduced-MII (Reverse-RMII) for glueless MAC-to-MAC connections to any MCU with Ethernet MAC MII or RMII interface. In addition, the EMI can be configured to Dual-PHY mode allowing AX88172A to act as an Ethernet PHY or USB 2.0 PHY for external MAC device that needs Ethernet and USB interfaces in their system applications. The optional serial interface such as I2C, SPI, and UART are provided as a control channel from the USB Host Controller to communicate with the external MCU chip.