General Description

The 78Q2120C is a form, fit and function replacement for the popular 78Q2120-64CGT 10BASE-T/100BASE-TX Fast Ethernet transceiver. It includes integrated MII, ENDECs, scrambler/descrambler, dual-speed clock recovery, and full-featured auto-negotiation functions.

The transmitter includes an on-chip pulse-shaper and a low-power line driver. The receiver has an adaptive equalizer and a baseline restoration circuit required for accurate clock and data recovery. The transceiver interfaces to Category-5 unshielded twisted pair (Cat-5 UTP) cabling for 100BASE-TX/10BASE-T and Category-3 unshielded twisted pair for 10BASE-T, and is connected to the line media via 1:1 isolation transformers. No external filter is required.


  • 10BASE-T/100BASE-TX IEEE-802.3 compliant TX and RX functions requiring a dual 1:1 isolation transformer interface to the line
  • Integrated MII, 10BASE-T/100BASE-TX ENDEC, 100BASE-TX scrambler/descrambler, and full-featured auto-negotiation function
  • Full duplex operation capable
  • PCS Bypass supports 5-bit symbol interface
  • Register-programmable transmit amplitude
  • Dual speed digital clock recovery
  • Automatic polarity correction during auto-negotiation and 10BASE-T signal reception
  • Power-saving and power-down modes including transmitter disable
  • LED indicators: LINK,TX,RX,COL,100,10,FDX
  • User programmable Interrupt pin
  • 64-Pin LQFP package
  • Single 3.3 V +/- 0.3V supply