LXT974/LXT975 — Fast Ethernet 10/100 Quad Transceivers
Figure 5. LXT975 Switch Application
Fiber
Module
Backplane
Fiber
Module
LXT974
10/100
Quad Transceiver
Switch
MAC ASIC
Memory
Fiber
Module
Fiber
Module
LXT975
LXT975
LXT975
LXT975
10/100 Quad
Transceiver
10/100 Quad
Transceiver
10/100 Quad
Transceiver
10/100 Quad
Transceiver
QUAD
QUAD
QUAD
QUAD
Transformer
Transformer
Transformer
Transformer
Stacked RJ-45
10 or 100 Mbps
2.2
Network Media / Protocol Support
The LXT974/975 supports both 10BASE-T and 100BASE-TX Ethernet over twisted-pair, or 100
Mbps Ethernet over fiber media (100BASE-FX). A Media Independent Interface (MII) is used for
communication with the Media Access Controller (MAC).
2.2.1
10/100 Mbps Network Interface
Each of the four network interface ports consists of four external pins (two differential signal
pairs). The pins are shared between twisted-pair (TP) and fiber. Signal assignments (input or
output, positive or negative) vary depending on whether the port is configured for TP or fiber
media. Refer to Table 1 through Table 6 for specific pin assignments.
The LXT974/975 output drivers generate either 100BASE-TX, 10BASE-T, or 100BASE-FX
output. When not transmitting data, the LXT974/975 generates 802.3-compliant link pulses or idle
code. Input signals are decoded either as a 100BASE-TX, 100BASE-FX, or 10BASE-T input,
depending on the mode selected. Auto-negotiation/parallel detection or manual control is used to
determine the speed of this interface.
2.2.1.1
Twisted-Pair Interface
When operating at 100 Mbps, MLT3 symbols are continuously transmitted and received. When not
transmitting data, the LXT974/975 generates “IDLE” symbols.
During 10 Mbps operation, Manchester-encoded data is exchanged. When no data is being
exchanged, the line is left in an idle state.
In 100 Mbps mode, the LXT974/975 is capable of driving a 100BASE-TX connection over 100Ω,
Category 5, Unshielded Twisted Pair (UTP). A 10BASE-T connection can be supported using
100Ω Category 3, UTP.
20
Datasheet
INTEL [ INTEL ]
