XRT75L00D Datasheet, PDF (31/92 Pages) Exar Corporation – E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER

REV. 1.0.2
XRT75L00D
E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
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.
4.3 TRANSMIT PULSE SHAPER:
The Transmit Pulse Shaper converts the B3ZS encoded digital pulses into a single analog Alternate Mark
Inversion (AMI) pulse that meet the industry standard mask template requirements for STS-1 and DS3. See
Figure 8 and Figure 9.
For E3 mode, the pulse shaper converts the HDB3 encoded pulses into a single full amplitude square shaped
pulse with very little slope. This is illustrated in Figure 7.
The Pulse Shaper Block also consists of a Transmit Build Out Circuit, which can either be disabled or enabled
by setting the TxLEV input pin “High” or “Low” (in Hardware Mode) or setting the TxLEV bit to “1” or “0” in the
control register (in Host Mode).
For DS3/STS-1 rates, the Transmit Build Out Circuit is used to shape the transmit waveform that ensures that
transmit pulse template requirements are met at the Cross-Connect system. The distance between the
transmitter output and the Cross-Connect system can be between 0 to 450 feet.
For E3 rate, since the output pulse template is measured at the secondary of the transformer and since there is
no Cross-Connect system pulse template requirements, the Transmit Build Out Circuit is always disabled.
4.3.1 Guidelines for using Transmit Build Out Circuit:
If the distance between the transmitter and the DSX3 or STSX-1, Cross-Connect system, is less than 225 feet,
enable the Transmit Build Out Circuit by setting the TxLEV input pin “Low” (in Hardware Mode) or setting the
TxLEV control bit to “0” (in Host Mode).
If the distance between the transmitter and the DSX3 or STSX-1 is greater than 225 feet, disable the Transmit
Build Out Circuit.
4.3.2 Interfacing to the line:
The differential line driver increases the transmit waveform to appropriate level and drives into the 75Ω load as
shown in Figure 6.
4.4 Transmit Drive Monitor:
This feature is used for monitoring the transmit line for occurrence of fault conditions such as short circuit on
the line or defective line driver.The device can also be configured for internal tranmit driver monitoring.
To monitor the transmitter output of another chip, connect MTIP pin to the TTIP line via a 270 Ω resistor and
MRing pins to TRing line via 270 Ω resistor as shown in Figure 16
In order to configure the device for internal transmit driver monitoring, set the TxMON bit to “1” in the transmit
control register.
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