LU3X34FTR Datasheet, PDF (22/52 Pages) Agere Systems – Quad 3 V 10/100 Ethernet Transceiver TX/FX

LU3X34FTR
Quad 3 V 10/100 Ethernet Transceiver TX/FX
Preliminary Data Sheet
July 2000
Functional Description (continued)
Scrambler Block
For 100Base-TX applications, the scrambler is required
to control the radiated emissions at the media connec-
tor and on the twisted-pair cable.
The LU3X34FTR implements a data scrambler as
defined by the TP-PMD stream cipher function. The
scrambler uses an 11-bit ciphering linear feedback shift
register (LFSR) with the following recursive linear func-
tion:
X[n] = X[n – 11] + X[n – 9] (modulo 2)
The output of the LFSR is combined with data from the
encoder via an exclusive-OR logic function. By scram-
bling the data, the total energy launched onto the cable
is randomly distributed over a wide frequency range.
A seed value for the scrambler function can be loaded
by setting bit 4 of register 18h. When this bit is set, the
contents of bits [10:0] of register 19h (that are com-
posed of the 5-bit PHY address and a 6-bit user seed)
will be loaded into the LFSR. By specifying unique
seed value for each PHY in a system, the total EMI
energy produced by a repeater application can be
reduced.
Parallel-to-Serial and NRZ-to-NRZI Conversion
After the transmit data stream is scrambled, data is
loaded into a shift register and clocked out with a
125 MHz clock into a serial bit stream. The serialized
data is further converted from NRZ-to-NRZI format,
which produces a transition on every logic one and no
transition on logic zero.
Collision Detect
During 100 Mbits/s half-duplex operation, collision con-
dition is detected if the transmitter and receiver become
active simultaneously. Collision detection is indicated
by the COL signal of the internal MII. For full-duplex
applications, the COL signal is never asserted.
100Base-X Receiver
The 100Base-X receiver consists of functional blocks
required to recover and condition the 125 Mbits/s
receive data stream. The LU3X34FTR implements the
100Base-X receive state machine diagram as given in
ANSI/IEEE Standard 802.3u, Clause 24. The
125 Mbits/s receive data stream may originate from the
on-chip twisted-pair transceiver in a 100Base-TX appli-
cation. Alternatively, the receive data stream may be
generated by an external optical receiver as in a
100Base-FX application.
The receiver block consists of the following functional
blocks:
s Equalizer.
s Clock recovery module.
s NRZI/NRZ and serial/parallel decoder.
s Descrambler.
s Symbol alignment block.
s Symbol decoder.
s Collision detect block.
s Carrier sense block.
s Stream decoder block.
Clock Recovery
The clock recovery module accepts 125 Mbits/s scram-
bled NRZI data stream from either the on-chip
100Base-TX receiver or from an external 100Base-FX
transceiver. The LU3X34FTR uses an onboard digital
phase-locked loop (PLL) to extract clock information of
the incoming NRZI data, which is then used to retime
the data stream and set data boundaries.
After power-on or reset, the PLL locks to a free-running
25 MHz clock derived from the external clock source.
When initial lock is achieved, the PLL switches to lock
to the data stream, extracts a 125 MHz clock from the
data, and uses it for bit framing of the recovered data.
NRZI-to-NRZ and Serial-to-Parallel Conversion
The recovered data is converted from NRZI to NRZ.
The data is not necessarily aligned to 4B/5B code-
group’s boundary.
Data Descrambling
The descrambler acquires synchronization with the
data stream by recognizing idle bursts of 40 or more
bits and locking its deciphering linear feedback shift
register (LFSR) to the state of the scrambling LFSR.
Upon achieving synchronization, the incoming data is
XORed by the deciphering LFSR and descrambled.
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Lucent Technologies Inc.