English
Language : 

XRT73L02M Datasheet, PDF (26/46 Pages) Exar Corporation – TWO CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT
XRT73L02M
xr
TWO CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT
REV. 1.0.0
4.0.1 TRANSMIT CLOCK:
The Transmit Clock applied via TxClk_n pins, for the selected data rate (for E3 = 34.368 MHz, DS3 = 44.736
MHz or STS-1 = 51.84 MHz), is duty cycle corrected by the internal PLL circuit to provide a 50% duty cycle
clock to the pulse shaping circuit. This allows a 30% to 70% duty cycle Transmit Clock to be supplied.
4.0.2 B3ZS/HDB3 ENCODER:
When the Single-Rail (NRZ) data format is selected, the Encoder Block encodes the data into either B3ZS for-
mat (for either DS3 or STS-1) or HDB3 format (for E3).
4.0.2.1 B3ZS Encoding:
An example of B3ZS encoding is shown in Figure 14. If the encoder detects an occurrence of three consecu-
tive zeros in the data stream, it is replaced with either B0V or 00V, where ‘B’ refers to Bipolar pulse that is com-
pliant 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
TClk
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
0
1
V
B
V
4.0.2.2 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 consecu-
tive 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
B
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.
24