Data Sheet

Ethernet Controller I210 —Interconnects
126
The scrambler is driven by a 33-bit Linear Feedback Shift Register (LFSR), which is randomly loaded at
power up. The LFSR function used by the master differs from that used by the slave, giving each
direction its own unique signature. The LFSR, in turn, generates twelve mutually uncorrelated outputs.
Eight of these are used to randomize the inputs to the 4DPAM5 and Trellis encoders. The remaining four
outputs randomize the sign of the 4DPAM5 outputs.
3.7.8.7.2.2 Transmit FIFO
The transmit FIFO re-synchronizes data transmitted by the MAC to the transmit reference used by the
PHY. The FIFO is large enough to support a frequency differential of up to +/- 1000 ppm over a packet
size of 10 KB (jumbo frame).
3.7.8.7.2.3 Transmit Phase-Locked Loop PLL
This function generates the 125 MHz timing reference used by the PHY to transmit 4DPAM5 symbols.
When the PHY is the master side of the link, the XI input is the reference for the transmit PLL. When the
PHY is the slave side of the link, the recovered receive clock is the reference for the transmit PLL.
3.7.8.7.2.4 Trellis Encoder
The Trellis encoder uses the two high-order bits of data and its previous output to generate a ninth bit,
which determines if the next 4DPAM5 pattern should be even or odd.
For data, this function is:
Trellisn = Data7n-1 XOR Data6n-2 XOR Trellisn-3
This provides forward error correction and enhances the Signal-To-Noise (SNR) ratio by a factor of 6
dB.
3.7.8.7.2.5 4DPAM5 Encoder
The 4DPAM5 encoder translates 8-byte codes transmitted by the MAC into 4DPAM5 symbols. The
encoder operates at 125 MHz, which is both the frequency of the MAC interface and the baud rate used
by 1000BASE-T.
Each 8-byte code represents one of 28 or 256 data patterns. Each 4DPAM5 symbol consists of one of
five signal levels (-2,-1,0,1,2) on each of the four twisted pair (A,B,C,D) representing 54 or 625
possible patterns per baud period. Of these, 113 patterns are reserved for control codes, leaving 512
patterns for data. These data patterns are divided into two groups of 256 even and 256 odd data
patterns. Thus, each 8-byte octet has two possible 4DPAM5 representations: one even and one odd
pattern.
3.7.8.7.2.6 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.