LXT975 datasheet(19/74 Pages) INTEL

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Fast Ethernet 10/100 Quad Transceivers — LXT974/LXT975

Datasheet

2.0

Functional Description

2.1

Introduction

The LXT974 and LXT975 are four-port Fast Ethernet 10/100 Transceivers that support 10 Mbps

and 100 Mbps networks. They comply with all applicable requirements of IEEE 802.3. Each port

can directly drive either a 100BASE-TX line (>130 meters) or a 10BASE-T line (>185 meters).

Figure 4 shows the LXT974 in a typical switch application.

On power-up, the LXT974/975 uses auto-negotiation/parallel detection on each port to

automatically determine line operating conditions. If the PHY device on the other side of the link

supports auto-negotiation, the LXT974/975 auto-negotiates with it using Fast Link Pulse (FLP)

Bursts. If the PHY partner does not support auto-negotiation, the LXT974/975 automatically

detects the presence of either link pulses (10 Mbps PHY) or Idle symbols (100 Mbps PHY) and set

its operating conditions accordingly.

The LXT974/975 interfaces to four 10/100 Media Access Controllers (MAC)s through the MII

interfaces. It performs all functions of the Physical Coding Sublayer (PCS) and Physical Media

Attachment (PMA) sublayer as defined in the IEEE 802.3 100BASE-X specification. This device

also performs all functions of the Physical Media Dependent (PMD) sublayer for 100BASE-TX

connections. The MII speeds are automatically set once port operating conditions have been

determined.

The LXT974/975 provides half-duplex and full-duplex operation at 100 Mbps and 10 Mbps. It also

offers standard Loopback Mode for switch applications. The LXT974/975 supports the 802.3

MDIO register set. Specific bits in the registers are referenced using an “X.Y” notation, where X is

the register number (0-6 or 16-20) and Y is the bit number (0-15).

The LXT975 is pin compatible with the LXT974 except for the network ports. Each port on the

LXT974 provides a combination twisted-pair or PECL interface for a 10/100BASE-TX or

100BASE-FX connection.

The LXT975 is optimized for stacked RJ-45 modular applications as shown in Figure 5. Ports 1

and 3 support the PECL interface for fiber connections and all four ports support the twisted-pair

interface for 10/100BASE-TX connections.

Figure 4. LXT974 Switch Application

Single RJ-45

Selectable 10 or 100 Mbps

Fiber

Module

Backplane

Memory

Fiber

Module

Fiber

Module

Fiber

Module

LXT974

10/100

Quad Transceiver

Switch

MAC ASIC

LXT974

10/100

Quad Transceiver

LXT974

10/100

Quad Transceiver

QUAD

Transformer

QUAD

Transformer

LXT975 Datasheet(PDF) 19 Page - Intel Corporation

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