XRT7300 datasheet(41/55 Pages) EXAR

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XRT7300

E3/DS3/STS-1 LINE INTERFACE UNIT

REV. 1.1.1

If the XRT7300 is operating in the HOST Mode:

Access the Microprocessor Serial Interface and write

a “1” into the LLB bit-field and a “0” into the RLB bit-

field in Command Register 4.

If the XRT7300 is operating in the Hardware

Mode:

The LLB input pin (pin 14) must be set to “High” and

the RLB input pin (pin 15) must be set to “Low”.

NOTES:

1. The Analog Local Loop-Back Mode does not work

if the transmitter is turned off via the TXOFF fea-

ture.

2. The XRT7300 automatically Declares an LOS Con-

dition anytime it has been configured to operate in

either the Analog Local Loop-Back or Digital Local

Loop-Back Modes. Consequently, the MUTing -

upon -LOS must be disabled prior to configuring

the device to operate in either of these local Loop-

Back modes.

4.2

THE DIGITAL LOCAL LOOP-BACK MODE

When the XRT7300 is configured to operate in the

Digital Local Loop-Back Mode, it ignores any signals

that are input to the RTIP and RRING input pins. The

Transmitting Terminal Equipment transmits clock and

data into the XRT7300 via the TPDATA, TNDATA and

TCLK input pins. This data is processed through the

Transmit Clock Duty Cycle Adjust PLL and the HDB3/

B3ZS Encoder block and then looped back to the

HDB3/B3ZS Decoder block.

Figure 29 illustrates the path that the data takes when

the chip is configured to operate in the Digital Local

Loop-Back Mode.

FIGURE 28. THE ANALOG LOCAL LOOP-BACK IN THE XRT7300

AGC/

Equalizer

Peak

Detector

LOS Detector

Slicer

Clock

Recovery

Data

Recovery

Invert

Loop MUX

HDB3/

B3ZS

Decoder

LOSTHR

SDI

SDO/LCV

SCLK

REGRESET

RTIP

RRING

REQDIS

RCLK1

RCLK2

RPOS

RNEG

DECODIS

RLOS

LLB

RLB

ENCODIS

TAOS

TPDATA

TNDATA

TCLK

RLOL EXCLK

Device

Monitor

MTIP

MRING

Transmit

Logic

Duty Cycle Adjust

TXLEV

TXOFF

DMO

TTIP

TRING

Pulse

Shaping

HDB3/

B3ZS

Encoder

Serial

Processor

Interface

Analog Local

Loop-Back Path

COMMAND REGISTER CR4 (ADDRESS = 0X04)

STS-1/DS3

LLB

RLB

XRT7300 Datasheet(PDF) 41 Page - Exar Corporation

XRT7300 Datasheet(HTML) 41 Page - Exar Corporation

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