
Intel
 
LXT9785 and Intel
 LXT9785E 
Advanced 8-Port 10/100 Mbps PHY 
Transceivers
Datasheet
The Intel
 LXT9785 and Intel
 LXT9785E are 8-port Fast Ethernet PHY Transceivers 
supporting IEEE 802.3 physical layer applications at 10 Mbps and 100 Mbps. These devices 
provide Serial/Source Synchronous Serial Media Independent Interfaces (SMII/SS-SMII) and 
Reduced Media Independent Interface (RMII) for switching and other independent port 
applications. The LXT9785 and LXT9785E are identical except for the IP telephony features 
included in the LXT9785E transceiver. The LXT9785E is an enhanced version of the LXT9785 
that detects Data Terminal Equipment (DTE) requiring power from the switch over a CAT5 
cable. The system uses the information collected by the LXT97985E to apply power if the DTE 
at the far end requires power over the cable, such as an IP telephone.
Each network port can provide a twisted-pair (TP) or Low-Voltage Positive Emitter Coupled 
Logic (LVPECL) interface. The twisted-pair interface supports 10 Mbps and 100 Mbps 
(10BASE-T and 100BASE-TX) Ethernet over twisted-pair. The LVPECL interface supports 
100 Mbps (100BASE-FX) Ethernet over fiber-optic media.
The LXT9785/LXT9785E provides three discrete LED driver outputs for each port. The devices 
support both half-duplex and full-duplex operation at 10 Mbps and 100 Mbps and require only a 
single 2.5 V power supply. 
Applications
Product Features
 Enterprise switches
 IP telephony switches
 Storage Area Networks
 Multi-port Network Interface Cards (NICs)
 Eight IEEE 802.3-compliant 10BASE-T or 
100BASE-TX ports with integrated filters.
 100BASE-FX fiber-optic capability on all 
ports.
 2.5 V operation.
 Low power consumption; 250 mW per port 
typical.
 Multiple RMII or SMII/SS-SMII ports for 
independent PHY port operation.
 Auto MDI/MDIX crossover capability.
 Proprietary Optimal Signal Processing 
architecture improves SNR by 3 dB over 
ideal analog filters.
 Optimized for dual-high stacked RJ-45 
applications.
 MDIO sectionalization into 2x4 or 1x8 
configurations.
 Supports both auto-negotiation systems and 
legacy systems without auto-negotiation 
capability.
 Robust baseline wander correction.
 Configurable through the MDIO port or 
external control pins.
 JTAG boundary scan.
 208-pin PQFP: LXT9785HC, 
LXT9785EHC, LXT9785HE.
 241-ball BGA: LXT9785BC, 
LXT9785EBC.
 196-ball BGA: LXT9785MBC
 DTE detection for remote powering 
applications (LXT9785E only).
 Extended temperature operation of -40
o
C to 
+85
o
C (LXT9785HE).
Document Number: 249241
Revision Number: 007
Revision Date: August 28, 2003