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202 Software Developer’s Manual
PHY Functionality and Features
11.11.3.4 Spectral Shaper
This function causes the 4DPAM5 waveform to have a spectral signature that is very close to that
of the MLT3 waveform used by 100BASE-TX. This enables 1000BASE-T to take advantage of
infrastructure (cables, magnetics) designed for 100BASE-TX.
The shaper works by transmitting 75% of a 4DPAM5 code in the current baud period, and adding
the remaining 25% into the next baud period.
11.11.3.5 Low-Pass Filter
To aid with EMI, this filter attenuates signal components more than 180 Mhz. In 1000BASE-T, the
fundamental symbol rate is 125 Mhz.
11.11.3.6 Line Driver
The line driver drives the 4DPAM5 waveforms onto the four twisted-pair channels (A, B, C, D),
adding them onto the waveforms that are simultaneously being received from the link partner.
11.11.3.7 Transmit/Receive Flow
Scrambler Polynomials:
1 + x
13
+ x
33
(Master PHY Mode)
1 + x
20
+ x
33
(Slave PHY Mode)
Figure 11-4. 1000BASE-T Transmit Flow And Line Coding Scheme
D0
D1
D2
D3
D4
D5
D6
D7
Scrambler
Trellis
Encoder
4D
PAM-5
PAM-5
Encoded Output
to 4-Pair UPT Line
8
9