LXT970ATC datasheet(39/74 Pages) INTEL

39 / 74 page

Dual-Speed Fast Ethernet Transceiver — LXT970A

Datasheet

For 10T links, CRS assertion is based on reception of valid preamble, and de-assertion on reception

of an end-of-frame (EOF) marker.

The PMA layer in the LXT970A does not support the optional Far-End-Fault function.

2.8.3

Twisted-Pair PMD Layer

The twisted-pair Physical Medium Dependent (PMD) layer provides the signal scrambling and

descrambling, line coding and decoding (MLT-3 for 100TX, Manchester for 10T), as well as

receiving, polarity correction, and baseline wander correction functions.

2.8.3.1

Scrambler/Descrambler (100TX Only)

The scrambler spreads the signal power spectrum and reduces EMI and baseline wander.

Scrambling is done with an 11-bit, non-data-dependent polynomial. The receiver automatically

decodes the polynomial whenever IDLE symbols are received.

The LXT970A provides a scrambler-bypass mode for testing purposes. Bypassing the scrambler

causes the PCS-layer encoder to be bypassed as well, and the MII to operate in 5B mode.

2.8.3.2

Baseline Wander Correction

(100TX Only)

The LXT970A provides a baseline wander correction function that makes the device robust under

all network operating conditions. The MLT3 coding scheme used in 100BASE-TX is by definition

“unbalanced”, which means the average DC value of the signal voltage can “wander” significantly

over short time intervals (tenths of seconds). In less robust PHY devices, this wander can cause

receiver errors, particularly at long line lengths (100 meters). The exact characteristics of the

wander are completely data dependent. The LXT970A baseline wander correction circuitry allows

error-free data recovery, even at long line lengths.

2.8.3.3

Polarity Correction

The LXT970A automatically detects and corrects for the condition where the receive signal (TPIP/

N) is inverted. Reversed polarity is detected if eight inverted link pulses, or four inverted end-of-

frame markers, are received consecutively. If link pulses or data are not received for 96-128 ms,

the polarity state is reset to a non-inverted state.

2.8.4

Fiber PMD Layer

The LXT970A provides a pseudo-ECL interface for connection to an external fiber optic

transceiver. (The external transceiver provides the PMD function for fiber media.) The LXT970A

uses an NRZI format for the fiber interface. The fiber interface operates at 100 Mbps and is

intended for 100FX applications. It does not support 10FL applications. The fiber interface does

not support the signal detect function supplied by most fiber optic transceivers. However, the link

detection function in the PMA layer quickly detects faults in the fiber link.

LXT970ATC 数据表(PDF) 39 Page - Intel Corporation

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