XRT72L50 Datasheet, PDF (128/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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2. The user is advised to disable the B3ZS/HDB3 encoder (within the LIU IC) if the channel is configured to operate
in the B3ZS/HDB3 line code.
3. If the customer is not using an Exar XRT73L0X DS3/E3/STS-1 LIU IC, then this bit-field and the Encodis output
pin can be used for other purposes.
Bit 2 - TxLev - (Transmit Output Line Build-Out Select Output)
This Read/Write bit-field permits the user to control the state of the TxLev[n] output pin of the Framer. This
output pin is intended to be connected to the TxLev input pin of the DS3/E3 LIU IC. If the user commands this
signal to toggle "High", then the DS3/E3 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 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 LIU meet the DSX-3 Isolated Pulse Template
Requirements (per Bellcore GR-499-CORE), the user is advised to set this bit-field to "0", if the length of cable
(between the LIU transmit output 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 LIU transmit output
and the DSX-3 Cross Connect system) 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".
NOTES:
1. The TxLEV function is only applicable to DS3 applications. E3 LIUs do not support this kind of Line Build out
feature.
2. If the customer is not using an Exar XRT73L0X DS3/E3 LIU IC, then this bit-field and the TxLev output pin can be
used for other purposes.
Bit 1 - RLOOP - (Remote Loop-back)
This Read/Write bit-field permits the user to control the state of the RLOOP[n] output pin of the Framer. This
output pin is intended to be connected to the RLOOP input pin of the DS3/E3 LIU IC.
When using Exar’s family of XRT73L0X DS3/E3 LIUs, the state of the RLOOP and the LLOOP pins are used
to dictate which loop-back mode the LIU 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 DS3/E3 LIU
0
0
Normal Operation (No Loop-back Mode)
0
1
Analog Local Loop-back Mode
1
0
Remote Loop-back Mode
1
1
Digital Local Loop-back Mode
Writing a "1" into this bit-field commands the Framer IC to toggle the RLOOP[n] output signal "High". Writing a
"0" into this bit-field commands the Framer IC to toggle this output signal "Low".
For a detailed description on the operation of a particular Exar XRT73L0X DS3/E3 LIU, while configured into
each of these above-mentioned loop-back modes, please consult the appropriate LIU Data Sheet.
NOTE: If the customer is not using an Exar XRT73L0X DS3/E3/STS-1 LIU IC, then this bit-field and the RLOOP[n] output
pin can be used for other purposes.
Bit 0 - LLOOP - (Local Loop-back)
This Read/Write bit-field permits the user to control the state of the LLOOP[n] output pin of the Framer. This
output pin is intended to be connected to the LLOOP input pin of the DS3/E3 LIU IC.
When using Exar’s family of XRT73L0X DS3/E3 LIUs, the state of the RLOOP and the LLOOP pins are used to
dictate which loop-back mode the LIU will operate in. The previous 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 to toggle the LLOOP[n] output signal "High". Writing a "0"
into this bit-field commands the Framer to toggle this output signal "Low".
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