DP83620SQ Datasheet, PDF (56/105 Pages) Texas Instruments – DP83620 Industrial Temperature Single Port 10/100 Mbps Ethernet Physical Layer

DP83620
SNLS339C – JANUARY 2011 – REVISED APRIL 2013
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7.2.3 Signal Detect
The signal detect function of the DP83620 is incorporated to meet the specifications mandated by the
ANSI FDDI TP-PMD Standard as well as the IEEE 802.3 100BASE-TX Standard for both voltage
thresholds and timing parameters.
Note that the reception of normal 10BASE-T link pulses and fast link pulses per IEEE 802.3u Auto-
Negotiation by the 100BASE-TX receiver do not cause the DP83620 to assert signal detect.
7.2.4 MLT-3 to Binary Decoder
The DP83620 decodes the MLT-3 information from the Digital Adaptive Equalizer block to binary NRZI
data.
7.2.5 Clock Recovery Module
The Clock Recovery function is implemented as a Phase detector and Loop Filter which accepts data and
error from the receive datapath to detect the phase of the recovered data. This phase information is fed
into the loop filter to determine an 8-bit signed frequency control. The 8-bit signed frequency control is
sent to the FCO in the Analog Front End to derive the receive clock. The extracted and synchronized
clock and data are used as required by the synchronous receive operations as generally depicted in
Figure 7-2.
7.2.6 NRZI to NRZ Decoder
In a typical application, the NRZI to NRZ decoder is required in order to present NRZ formatted data to the
descrambler (or to the code-group alignment block if the descrambler is bypassed).
7.2.7 Serial to Parallel
The 100BASE-TX receiver includes a Serial to Parallel converter which supplies 5-bit wide data symbols
to the PCS Rx state machine.
7.2.8 Descrambler
A serial descrambler is used to de-scramble the received NRZ data. The descrambler has to generate an
identical data scrambling sequence (N) in order to recover the original unscrambled data (UD) from the
scrambled data (SD) as represented in the equations:
Synchronization of the descrambler to the original scrambling sequence (N) is achieved based on the
knowledge that the incoming scrambled data stream consists of scrambled IDLE data. After the
descrambler has recognized 12 consecutive IDLE code-groups, where an unscrambled IDLE code-group
in 5B NRZ is equal to five consecutive ones (11111), it will synchronize to the receive data stream and
generate unscrambled data in the form of unaligned 5B code-groups.
In order to maintain synchronization, the descrambler must continuously monitor the validity of the
unscrambled data that it generates. To ensure this, a line state monitor and a hold timer are used to
constantly monitor the synchronization status. Upon synchronization of the descrambler, the hold timer
starts a 722 µs countdown. Upon detection of sufficient IDLE code-groups (58 bit times) within the 722 µs
period, the hold timer will reset and begin a new countdown. This monitoring operation will continue
indefinitely given a properly operating network connection with good signal integrity. If the line state
monitor does not recognize sufficient unscrambled IDLE code-groups within the 722 µs period, the entire
descrambler will be forced out of the current state of synchronization and reset in order to re-acquire
synchronization. The DP83604T also provides a bit (DESC_TIME, bit 7) in the PCSR register (0x16) that
increases the descrambler timeout from 722 µs to 2 ms to allow reception of packets up to 9kB in size
without losing descrambler lock.
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Architecture
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