LXT974/LXT975 — Fast Ethernet 10/100 Quad Transceivers
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
2.5.7
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.
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
2.6.2
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.
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.
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Datasheet
INTEL [ INTEL ]
