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LXT974A

Fast Ethernet 10/100 Quad Transceivers

Intel 

LXT974/LXT975 — Fast Ethernet 10/100 Quad Transceivers

Figure 5. LXT975 Switch Application

Fiber

Module

Fiber

Module

Fiber

Module

Fiber

Module

Backplane

LXT974

10/100

Quad Transceiver

Switch

MAC ASIC

Memory

LXT975

10/100 Quad

Transceiver

QUAD

Transformer

LXT975

10/100 Quad

Transceiver

QUAD

Transformer

LXT975

10/100 Quad

Transceiver

QUAD

Transformer

LXT975

10/100 Quad

Transceiver

QUAD

Transformer

Stacked RJ-45

10 or 100 Mbps

2.2

2.2.1

2.2.1.1

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).

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.

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

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