XRT72L13 datasheet(154/370 Pages) EXAR

154 / 370 page

XRT72L13

MULTIPLEXER/FRAMER IC

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PRELIMINARY

REV. 1.0.6

142

2. The user is advised to disabled the B3ZS/HDB3

encoder (within the XRT7300 IC) if the XRT72L13

is configured to operate in the B3ZS/HDB3 line

code.

3. If the customer is not using the XRT7300 DS3/E3/

STS-1 LIU IC, then he/she can use this bit-field and

the "Encodis" output pin for other purposes.

4. It is permissible to tie the "Encodis" output pin of

the XRT 72L13 DS3 Framer IC to both the "Enco-

dis" and "Decodis" input pins of the XRT7300.

Bit 2 - TxLev - (Transmit Output Line Build-Out

Select Output)

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

the state of the "TxLev" output pin of the XRT72L13.

This output pin is intended to be connected to the Tx-

Lev input pin of the XRT7300 DS3/E3/STS-1 LIU IC.

If the user commands this signal to toggle "high", then

the XRT7300 DS3/E3/STS-1 LIU IC will disable the

"Transmit Line Build-Out" circuitry, and will transmit

unshaped (square-wave) pulses onto the line. If the

user commands this signal to toggle "low", then the

XRT7300 DS3/E3 LIU IC will enable the "Transmit

Line Build-Out" circuitry, and will transmit shaped

pulses onto the line.

In order to insure that the transmit output pulses of

the XRT7300 meet the "DSX-3 Isolated Pulse Tem-

plate Requirements (per Bellcore GR-499-CORE),

the user is advised to set this bit-field to "0", if the

length of cable (between the XRT7300 transmit out-

put and the DSX-3 Cross Connect System) is greater

than 225 feet.

Conversely, the user is advised to set this bit-field to

"1", if the length of cable (between the XRT7300

transmit output and the DSX-3 Cross Connect sys-

tem) is less than 225 feet.

Writing a "1" to this bit-field commands the Framer to

toggle the TxLev output "high". Writing a "0" to this

bit-field commands the Framer to toggle this output

signal "low".

Bit 1 - RLOOP - (Remote Loopback)

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

the state of the RLOOP output pin of the XRT72L13

M13 device. This output pin is intended to be con-

nected to the "RLOOP" input pin of the XRT7300

DS3/E3 LIU IC.

In the XRT7300 DS3/E3 LIU IC, the state of the

"RLOOP" and the "LLOOP" pins are used to dictate

which loop-back mode the XRT7300 will operate in.

The following table presents the relationship between

the state of these two input pins (or bit-fields) and the

resulting loop-back modes.

Writing a "1" into this bit-field commands the Framer

IC to toggle the "RLOOP" output signal "high". Writ-

ing a "0" into this bit-field commands the Framer IC to

toggle this output signal "low".

For a detailed description of the XRT7300 DS3/E3

LIU's operation, during each of these above-men-

tioned loop-back modes, please consult 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 he/she can use this bit-field and the

"RLOOP" output pin for other purposes.

Bit 0 - LLOOP - (Local Loop-back)

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

the state of the LLOOP output pin of the XRT72L13

M13 device. This output pin is intended to be con-

nected to the LLOOP input pin of the XRT7300 DS3/

E3 LIU IC.

In the XRT7300 DS3/E3 LIU IC, the state of the

"RLOOP" and the "LLOOP" pins are used to dictate

which loop-back mode the XRT7300 will operate in.

The following table presents the relationship between

the state of these two input pins (or bit-fields) and the

resulting loop-back modes.

RLOOP

LLOOP

RESULTING LOOP-BACK MODE OF THE XRT7300

Normal Operation (No Loop-back Mode)

Analog Local Loop-back Mode

Remote Loop-back Mode

Digital Local Loop-back Mode

RLOOP

LLOOP

RESULTING LOOP-BACK MODE OF THE XRT7300

Normal Operation (No Loop-back Mode)

Analog Local Loop-back Mode

Remote Loop-back Mode

XRT72L13 Datasheet(PDF) 154 Page - Exar Corporation

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