SLXT973QE Cortina Systems Inc, SLXT973QE Datasheet - Page 58

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SLXT973QE

Manufacturer Part Number
SLXT973QE
Description
Manufacturer
Cortina Systems Inc
Datasheet

Specifications of SLXT973QE

Lead Free Status / RoHS Status
Not Compliant
LXT973 Transceiver
Datasheet
249426, Revision 6.0
13 July 2007
8.1.1
8.1.2
8.1.3
8.1.4
8.1.5
Figure 21
Cortina Systems
Scrambler Seeding
Once the transmit data (or IDLE symbols) are properly encoded, they are scrambled to
further reduce EMI and to spread the power spectrum using an 11-bit scrambler seed.
Five-seed bits are determined by global PHY address, and six-seed bits are selected by
the port number. One of the 11 bits must be a “1”.
Scrambler Bypass
The scrambler can be bypassed by setting Register bit 16.12 = 1. Scrambler Bypass is
provided for diagnostic and test support.
The descrambler cannot be bypassed. The 100BASE-TX receiver in the LXT973
Transceiver will not converge to unscrambled idle, so a descrambler bypass is useless.
100BASE-T Link Failure Criteria and Override
The LXT973 Transceiver normally transmits 100Mbps data packets only if it detects the
link is up, and transmits only Idle symbols or FLP bursts if the link is not up. Setting
Register bit 16.14 = 1 overrides this function, allowing the LXT973 Transceiver to transmit
data packets even when the link is down. This feature is provided as a diagnostic tool.
Note that auto-negotiation must be disabled to transmit data packets in the absence of
link. If auto-negotiation is enabled, the
LXT973 Transceiver automatically begins transmitting FLP bursts if the link goes down.
Baseline Wander Correction
The LXT973 Transceiver 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 at long line lengths (160 meters). The exact
characteristics of the wander are completely data dependent. “Killer Packets” have been
created that exhibit worst case baseline wander characteristics. The LXT973 Transceiver
baseline wander correction characteristics allow the LXT973 Transceiver to recover error-
free data, even at long line lengths.
Programmable Tx Slew Rate
The LXT973 Transceiver device supports a slew rate mechanism where one of four pre-
selected slew rates can be used, set either through the input pins or through Register 27.
100BASE-TX Reception with no Errors
®
LXT973 10/100 Mbps Dual-Port Fast Ethernet PHY Transceiver
RXD<3:0>
RXCLK
RXDV
RXER
preamble SFD SFD DA
DA
DA
DA
CRC
CRC
8.1 Displaying Symbol Errors
CRC
CRC
Page 58

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