
LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
Datasheet
117
Document Number: 249241
Revision Number: 010
Revision Date: 30-May-2006
4.2.1.1
Twisted-Pair Interface
The LXT9785/LXT9785E supports either 100BASE-TX or 10BASE-T connections over 100
Ω,
Category
5, Unshielded Twisted-Pair (UTP). Only a transformer, RJ-45, and bypass capacitors are
required to complete this interface. Using Intel's patented waveshaping technology, the transmitter
shapes the outgoing signal to help reduce the need for external EMI filters. Four slew rate settings
match the output waveform to the magnetic characteristics. Both transmit and receive terminations
are built into the LXT9785/LXT9785E so no external components are required between the
LXT9785/LXT9785E and the external transformer. The transmitter uses a transformer with a
center tap to help reduce power consumption.
When operating at 100 Mbps, MLT3 symbols are continuously transmitted and received. When not
transmitting data, the LXT9785/LXT9785E generates “IDLE” symbols.
During 10 Mbps operation, LXT9785/LXT9785E encoded data is exchanged. When no data are
being exchanged, the line is left in an idle state with NLPs transmitted to maintain link.
Figure 7. Interface Signals
TXENn
RXDn_0
TXDn_0
TXDn_1
RXDn_1
CRS_DVn
RXERn
DATA
Interface
MDDIS
MDCn
MDINTn
MDIOn
MDIO
Management
Interface
LEDn_2
LEDn_3
Port LEDs/
Controls
ADD[4:0]
TPFOPn
TPFONn
TPFIPn
TPFINn
Network
Interface
VCCIO
+3.3V
OR
+2.5V
VCCD
+2.5V
GNDD
.01uF
Addr &
MDIX/
Contr
Mode Select
MDIX_Enb
Direct Drive
TXCLK
RXCLK
LEDn_1
B3369-01