FLLXT1000BA.C4QE000 Intel, FLLXT1000BA.C4QE000 Datasheet - Page 59

• Manufacturer Part Number: FLLXT1000BA.C4QE000
• Manufacturer: Intel

Specifications of FLLXT1000BA.C4QE000

• Lead Free Status / RoHS Status: Not Compliant

2.6.2.3
2.6.2.4
2.6.2.5
2.6.3
2.6.3.1
Datasheet
Document #: 249276
Revision #: 002
Rev. Date: 07/20/01
MLT3 Encoder
The MLT3 encoder translates the encoded, scrambled data into an MLT3 waveform, which uses
three signal levels (+1, 0, -1) that follow each other in an infinitely repeating loop (+1 -> 0 -> -1 ->
0 -> +1). A “1” baud causes a transition to the next level in the sequence, a “0” baud causes the
sequence to remain at its present value. In order for the receive PLLs to function properly, a
minimum density of “1s” is needed. 5B symbols with excessive numbers of “0s” (generally
invalid) are avoided.
Link and Carrier Detector
The LXT1000 establishes a link whenever the scrambler becomes locked and remains locked for
approximately 50 ms. Whenever the scrambler loses lock (not receiving 12 idle symbols during a 2
ms window), the link is taken down. The result is a very robust operation, filtering out any small
noise “hits” that would otherwise disrupt the link. Furthermore, 100 Mbps idle patterns will not
bring up a 10 Mbps link.
Baseline Wander Correction
The LXT1000 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). If uncorrected, this wander can cause
receiver errors, particularly at long line lengths (100 meters). The exact characteristics of the
wander are completely data dependent. “Killer Packets” have been created that exhibit worst case
baseline wander characteristics. The LXT1000 baseline wander correction characteristics allow the
LXT1000 to recover error-free data, even at long line lengths.
Analog Functions
On the transmit side, the analog functions consist of a DAC and a filter. On the receiver, they
consist of an A/D, timing recovery, and AGC.
Transmitting/Receiving
The MAC asserts TX_EN and begins driving data on the TXD balls at the same time. The
LXT1000 substitutes a start-of-stream delimiter (/J/K symbol pair) for the first two nibbles sent by
the MAC (which are normally preamble - “55”). Then, it transparently encodes and scrambles the
rest of the frame until the MAC de-asserts TX_EN at the end of the packet. In response, the
LXT1000 drives an end-of-stream marker, /T/R, followed by idles, /I/I... (see
page
The LXT1000 receives a valid start-of-stream delimiter, asserts CRS and RX_DV to the MAC, and
immediately begins driving receive data on RXD<3:0>. It substitutes “55” (preamble) for the first
two bytes of SSD. It then continues to continuously descramble and decode the packet until it
encounters an end-of-stream marker, /T/R, at which point it de-asserts RX_DV and CRS (see
Figure 36 on page
Normal data transmission is implemented in 4-bit-wide (4B) nibbles to the MAC. If the 4B/5B
encoder is bypassed, 5B symbol data (instead of 4B nibbles) is passed to the MAC. RX_ER,
RX_DV, COL, and CRS signals continue to function as in normal 4B mode.
62).
62).
Gigabit Ethernet Transceiver — LXT1000
Figure 35 on
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