LXT975BHC datasheet(36/74 Pages) INTEL

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LXT974/LXT975 — Fast Ethernet 10/100 Quad Transceivers

Datasheet

2.5.6.2

Baseline Wander Correction

The LXT974/975 provides a baseline wander correction function which makes the device robust

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

definition “unbalanced”. This means that the DC average value of the signal voltage can “wander”

significantly over short time intervals (tenths of seconds). This wander can cause receiver errors,

particularly in less robust designs, at long line lengths (100 meters). The exact characteristics of the

wander are completely data dependent.

The LXT974/975 baseline wander correction characteristics allow the LXT974/975 to recover

error-free data while receiving worst-case “killer” packets over a variety of cable distances.

2.5.6.3

Polarity Correction

The LXT974/975 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 (EOF) markers, are received consecutively. If link pulses or data are not received by

the maximum receive time-out period, the polarity state is reset to a non-inverted state.

2.5.7

Fiber PMD Sublayer

The LXT974/975 provides a PECL interface for connection to an external fiber-optic transceiver.

(The external transceiver provides the PMD function for fiber media.) The LXT974/975 uses an

NRZI format for the fiber interface. The fiber interface operates at 100 Mbps and does not support

10FL applications.

2.6

10 Mbps Operation

The LXT974/975 operates as a standard 10BASE-T transceiver. Data transmitted by the MAC as

4-bit nibbles is serialized, Manchester-encoded, and transmitted on the TPOP/N outputs. Received

data is decoded and de-serialized into 4-bit nibbles. The LXT974/975 supports all the standard 10

Mbps functions.

2.6.1

10BASE-T MII Operation

The MAC transmits data to the LXT974/975 via the MII interface. The LXT974/975 converts the

digital data from the MAC into an analog waveform that is transmitted to the network via the

copper interface. The LXT974/975 converts analog signals received from the network into a digital

format suitable for the MAC. The LXT974/975 sends the received data to the MAC via the MII.

2.6.2

10BASE-T Network Operations

During 10BASE-T operation, the LXT974/975 transmits and receives Manchester-encoded data

across the network link. When the MAC is not actively transmitting data, the LXT974/975 sends

out link pulses on the line.

In 10BASE-T mode, the polynomial scrambler/descrambler is inactive. Manchester-encoded

signals received from the network are decoded by the LXT974/975 and sent across the MII to the

MAC.

LXT975BHC Datasheet(PDF) 36 Page - Intel Corporation

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