XRT7250 datasheet(144/463 Pages) EXAR

144 / 463 page

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

125

vised to set this bit-field to “1” if the cable length (be-

tween the transmit output of the XRT7300 device and

the DSX-3 Cross Connect System) is greater than

225 feet.

NOTE: If the customer is not using the XRT7300 DS3/E3/

STS-1 IC, then this bit-field and the TxLEV output pin can

be used for other purposes.

Bit 1 - RLOOP (Remote Loop-Back Select)

This Read/Write bit-field permits the user to control

the state of the RLOOP output pin of the Framer de-

vice. This output pin is intended to be connected to

the RLOOP input pin of the XRT73001 LIU IC.

The state of this bit-field (or pin) along with LLOOP

are used to configure the XRT7300 device into one of

four (4) loop-back modes. The relationship of the val-

ues of RLOOP, LLOOP and the resulting loop-back

mode (within the XRT7300 device) is tabulated below.

Writing a “1” into this bit-field commands the Framer

to drive the RLOOP output signal "High”. Writing a

“0” into this bit-field commands the Framer to drive

this output signal "Low”.

For a detailed description of the XRT7300 LIU’s oper-

ation during each of these loop-back modes, please

see the XRT7300 DS3/E3/STS-1 LIU IC data sheet.

NOTE: If the customer is not using the XRT7300 DS3/E3/

STS-1 LIU IC, then this bit-field and the RLOOP output pin

can be used for other purposes.

Bit 0 - LLOOP (Local Loop-back Select)

This Read/Write bit-field allows the user to control the

state of the LLOOP output pin of the Framer device.

This output pin is intended to be connected to the

LLOOP input pin of the XRT7300 DS3/E3/STS-1 LIU

IC.

The state of this bit-field (or pin) along with RLOOP

are used to configure the XRT7300 into one of four

(4) loop-back modes. The relationship of the values

of RLOOP, LLOOP and the resulting loop-back

modes (within the XRT7300 device) are presented in

Table 15.

Writing a “1” into this bit-field commands the Framer

to toggle the LLOOP output pin "High”. Writing a “0”

into this bit-field commands the Framer to toggle this

output signal "Low”.

For a detailed description of the XRT7300 LIU’s oper-

ation during each of these loop-back modes, please

see the XRT7300 DS3/E3/STS-1 LIU IC Data Sheet.

NOTE: If the customer is not using the XRT7300 DS3/E3/

STS-1 LIU IC, then this bit-field and the LLOOP output pin

can be used for other purposes.

3.2

BIT-FIELDS WITHIN THE LINE INTERFACE SCAN

The XRT7300 device contains three output pins

which can be made accessible to the Microprocessor

Interface, via the Line Interface Scan register. These

three output pins are listed below.

• DMO - Drive Monitor Output

• RLOL - Receive Loss of Lock Indicator

• RLOS - Receive Loss of Signal Indicator.

The logic state of each of these input pins (or output

pins from the LIU) can be monitored by reading the

contents of the Line Interface Scan register, as de-

picted below.

TABLE 15: THE RELATIONSHIP BETWEEN THE STATES OF RLOOP, LLOOP AND THE RESULTING LOOP-BACK MODE

WITH THE

XRT7300 DEVICE

RLOOP

LLOOP

RESULTING LOOP-BACK MODE (WITHIN THE XRT7300 DS3/E3/STS-1 LIU IC)

Normal Mode (No Loop-back)

Analog Local Loop-back Mode

Remote Loop-back Mode

Digital Local Loop-back Mode

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