user manual

198 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

+ x

(Master PHY Mode)

1 + x

+ x

(Slave PHY Mode)

Figure 11-4. 1000BASE-T Transmit Flow And Line Coding Scheme

Scrambler

Trellis

Encoder

PAM-5

Encoded Output

to 4-Pair UPT Line