78Q2120
10/100BASE-TX
Ethernet Transceiver
April 2000
DESCRIPTION
The 78Q2120 is a 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, and is connected to
the line media via 1:1 isolation transformers. No
external filter is required. Interface to the MAC is
accomplished through an IEEE-802.3 compliant
media independent interface (MII). The product is
fabricated in a BiCMOS process for high
performance and low power operation, and can
operate from a single 3.3 V or 5 V supply.

FEATURES
• 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
• Dual speed clock recovery
• Automatic polarity correction during auto-
negotiation and 10BASE-T signal reception
• Power-saving and power-down modes including
transmitter disable
• BiCMOS technology, operates with a single 3.3V or
5V supply
• LED indicators: LINK,TX,RX,COL,100,10,FDX
• User programmable Interrupt pin
• General Purpose I/O Interface (80-pin package
only)
• 64 and 80-Lead TQFP (JEDEC LQFP),
64-Pin QFP packages


BLOCK DIAGRAM
MII Serial
Management
& Control
Transmit
Adaptive EQ,
Baseline Wander Corrector,
MLT3 Decoder,
NRZI/NRZ
4B/5B Encoder,
Scrambler,
Parallel/Serial
MII
Registers
&
Interface
Logic
Parallel/Serial,
Manchester Encoder
Manchester Decoder,
Serial/Parallel
Serial/Parallel,
Descrambler,
5B/4B Decoder
NRZ/NRZI,
MTL3 Encoder
Pulse Shaper
& Filter
TX Clock
Generator
Carrier Sense,
Collision Detect
Auto
Negotiation
Clock
Recovery
Clock
Reference
UTP
Drivers
UTP
Receiver
LEDs
Vcc Ground
RXIP
RXIN
TXOP
TXON
LINK
TX
RX
COL
100BT
10BT
FDX
100M
100M
10M
10M
Receive
CKIN