XRT72L50 Datasheet, PDF (138/471 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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Bit 7 - ILOOP (Internal Remote Loop-back)
This Read/Write bit-field permits the user to configure the corresponding channel (within the XRT72L50) to
operate in the Internal Remote Loop-back Mode. Once the user configures the channel to operate in this
remote loop-back mode, then the RxPOSn, RxNEGn and RxLineClk signals will be routed directly to the
TxPOSn, TxNEGn and TxLineClk signals.
Setting this bit-field to “1” configures the channel to operate in the Remote Loop-Back Mode.
Bit 5 - REQB - (Receive Equalization Enable/Disable Select)
This Read/Write bit-field allows the user to control the state of the REQB output pin of the Framer. This output
pin is intended to be connected to the REQB input pin of the XRT73L0x DS3/E3/STS-1 LIU IC. If the user
forces this signal to toggle "High”, then the internal Receive Equalizer (within the XRT73L0x) will be disabled
for using short cable length. Conversely, if the user forces this signal to toggle "Low”, then the Receive
Equalizer (within the XRT73L0x) will be enabled for short cable length.
The purpose of the internal Receive Equalizer (within the XRT73L0x) is to compensate for the Frequency-
Dependent attenuation (e.g., cable loss), that a line signal will experience as it travels through coaxial cable,
from the transmitting to the receiving terminal.
Writing a “1” to this bit-field causes the Framer to toggle the REQB output pin "High”. Writing a “0” to this bit-
field causes the Framer to toggle the REQB output pin "Low”.
For information on the criteria that should be used when deciding whether to enable or disable the Receive
Equalizer, please consult the XRT73L0x DS3/E3/STS-1 LIU IC Data Sheet.
NOTE: If the customer is not using the XRT73L0x DS3/E3/STS-1 IC, then this bit-field and the REQB output pin can be
used for other purposes.
Bit 4 - TAOS - (Transmit All Ones Signal)
This Read/Write bit-field allows the user to control the state of the TAOS output pin of the Framer. This output
pin is intended to be connected to the TAOS input pin of the XRT73L0x DS3/E3/STS-1 LIU IC. if the user
forces this signal to toggle "High”, then the XRT73L0x will transmit an all 1’s pattern onto the line. Conversely,
if the user commands this output signal to toggle "Low” then the XRT73L0x DS3/E3/STS-1 LIU IC will proceed
to transmit data based upon the data that it receives via the TxPOS and TxNEG output pins (of the Framer IC).
Writing a “1” to this bit-field causes the TAOS output pin to toggle "High”. Writing a “0” to this bit-field will cause
this output pin to toggle "Low”.
NOTE: If the customer is not using the XRT73L0x DS3/E3/STS-1 LIU IC, then this bit-field, and the TAOS output pin can be
used for other purposes.
Bit 3 - ENCODIS - (B3ZS/HDB3 Encoder Disable)
This Read/Write bit-field allows the user to control the state of the ENCODIS output pin of the Framer. This
output pin is intended to be connected to the ENDECDIS input pin of the XRT73L0x DS3/E3/STS-1 LIU IC. If
the user forces this signal to toggle "High”, then the internal B3ZS/HDB3 encoder (within the XRT73L0x) will be
disabled. Conversely, if the user commands this output signal to toggle "Low”, then the internal B3ZS/HDB3
encoder (within the XRT73L0x) will be enabled.
Writing a “1” to this bit-field causes the Framer IC to toggle the Encodis output pin "High”. Writing a “0” to this
bit-field will cause the Framer IC to toggle this output pin "Low”.
NOTES:
1. The B3ZS/HDB3 encoder, within the XRT73L0x is not to be confused with the B3ZS/HDB3 encoding capabilities
that exists within the Transmit DS3/E3 Framer block of the Framer IC.
2. The user is advised to disable the B3ZS/HDB3 encoder (within the XRT73L0x IC) if the Transmit and Receive
DS3/E3 Framer (within the XRT72L50) are configured to operate in the B3ZS/HDB3 line code.
3. If the customer is not using the 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 Line Build-Out Enable/Disable Select)
This Read/Write bit-field allows the user to control the state of the TxLEV output pin of the Framer. This output
pin is intended to be connected to the TxLEV input pin of the XRT73L0x DS3/E3/STS-1 LIU IC.
Writing a “1” to this bit-field commands the Framer to drive the TxLEV output pin "High”.
Writing a “0” to this bit-field commands the Framer to drive this output signal "Low”.
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