This document introduces the 78Q21x3-DB design example, which is a 10/100BASE-TX Mbit/second Fast Ethernet MII interface adapter. Teridian 78Q2123 or 78Q2133 MicroPHY transceiver provides the network physical interface and MII (Medium Independent Interface) interface. Teridian Semiconductor’s MicroPHY is an auto-sensing, auto-switching 10/100BASE-TX Fast Ethernet transceiver with full duplex operation capability. The device interfaces directly to the IEEE-802.3u MII port. Full-featured MII management functions are included along with an extended register set. The MicroPHY five bit PHY address is defaulted to 0x001. The MicroPHY interfaces to CAT5 UTP cable via a 1:1 transformer. The transceiver’s transmitter includes on-chip the pulse shaper and low power line driver. The receiver incorporates a sophisticated combination of real-time adaptive equalization, an adaptive DC offset adjustment circuit and baseline wander correction. Smart squelch circuitry further improves the receiver’s noise rejection. Full featured auto-negotiation or parallel detect modes are supported. The demo board requires operation with a +3.3V power supply.