XRT75L04D Datasheet, PDF (31/98 Pages) Exar Corporation – FOUR CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER

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XRT75L04D
REV. 1.0.1 FOUR CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
4.2 B3ZS/HDB3 ENCODER:
When the Single-Rail (NRZ) data format is selected, the Encoder Block encodes the data into either B3ZS
format (for either DS3 or STS-1) or HDB3 format (for E3).
4.2.1 B3ZS Encoding:
An example of B3ZS encoding is shown in Figure 14. If the encoder detects an occurrence of three
consecutive zeros in the data stream, it is replaced with either B0V or 00V, where ‘B’ refers to Bipolar pulse that
is compliant with the Alternating polarity requirement of the AMI (Alternate Mark Inversion) line code and ‘V’
refers to a Bipolar Violation (e.g., a bipolar pulse that violates the AMI line code). The substitution of B0V or
00V is made so that an odd number of bipolar pulses exist between any two consecutive violation (V) pulses.
This avoids the introduction of a DC component into the line signal.
FIGURE 14. B3ZS ENCODING FORMAT
T C lk
TPDATA
Line
Signal
1 0 11
0 0 0 0 1 ^{0 00 0 0 0 0 0 0}
10
1 0 0V
1
0
00
B0V
1
V
B
0V
4.2.2 HDB3 Encoding:
An example of the HDB3 encoding is shown in Figure 15. If the HDB3 encoder detects an occurrence of four
consecutive zeros in the data stream, then the four zeros are substituted with either 000V or B00V pattern. The
substitution code is made in such a way that an odd number of bipolar (B) pulses exist between any
consecutive V pulses. This avoids the introduction of DC component into the analog signal.
FIGURE 15. HDB3 ENCODING FORMAT
TClk
TPDATA
Line
Signal
1 0 11 _{0 0 0 0 1} 0 0 0 0 0 0 0 0 0
10
1 0 0 _0V
000
B00V
1
1
V
NOTES:
1. When Dual-Rail data format is selected, the B3ZS/HDB3 Encoder is automatically disabled.
2. In Dual-Rail format, the Bipolar Violations in the incoming data stream is converted to valid data pulses.
3. Encoder and Decoder is enabled only in Single-Rail mode.
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