XRT75VL00D datasheet(31/92 Pages) EXAR

31 / 92 page

XRT75VL00D

REV. 1.0.3

E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER

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 75

Ω 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.

FIGURE 16. TRANSMIT DRIVER MONITOR SET-UP.

TT I P

TR i n g

X R T75V L00

1: 1

Ω

Tx PO S

Tx N E G

Tx L in e C lk

TP D a t a

T NDa t a

Tx C lk

Re x t

Re f A GND

31. 6

Ω + 1%

31 . 6

Ω +1%

MR i n g

MT I P

R5 2 7 0

Ω

R4 2 7 0

Ω

Tx P O S

Tx N E G

T x Li ne C l k

TPD a t a

TN D a t a

Tx C lk

Re x t

Re f A G N D

MR i n g

MT I P

TTI P

TR i n g

Ω

31. 6

Ω + 1%

31. 6

Ω +1%

1: 1

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