LXT975B datasheet(29/74 Pages) INTEL

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Fast Ethernet 10/100 Quad Transceivers — LXT974/LXT975

Datasheet

2.4

Auto-Negotiation

The LXT974/975 attempts to auto-negotiate with its counterpart across the link by sending Fast

Link Pulse (FLP) bursts. Each burst consists of 33 link pulses spaced 62.5

µs apart. Odd link

pulses (clock pulses) are always present. Even link pulses (data pulses) may be present or absent to

indicate a “1” or a “0”. Each FLP burst exchanges 16 bits of data, which are referred to as a

“page”. All devices that support auto-negotiation must support a “Base Page” as defined in the

IEEE 802.3 standard.

By exchanging Base Pages, the LXT974/975 and its link partner communicate their capabilities to

each other. Both sides must receive at least three identical base pages for negotiation to proceed.

Each side finds the highest common capabilities that both sides support. Both sides then exchange

more pages, and finally agree on the operating state of the line.

2.4.1

Parallel Detection

In parallel with auto-negotiation, the LXT974/975 also monitors for 10 Mbps Normal Link Pulses

(NLP) or 100 Mbps Idle symbols. If either is detected, the device automatically reverts to the

corresponding operating mode. Parallel detection allows the LXT974/975 to communicate with

devices that do not support auto-negotiation.

2.4.2

Controlling Auto-Negotiation

When auto-negotiation is controlled by software, the following steps are recommended:

• After power-up, power-down, or reset, the power- down recovery time, as specified in Table

41 on page 62, must be exhausted before proceeding.

• Set the auto-negotiation advertisement register bits.

• Enable auto-negotiation by setting MDIO

bit 0.12 = 1.

2.4.3

Monitoring Auto-Negotiation

When auto-negotiation is being monitored, the following apply:

• Bit 20.13 is set to 1 once the link is established.

• Bits 20.12 and 20.11 can be used to determine the link operating conditions (speed and

duplex).

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