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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
114
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.
N
OTE
:
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 permits 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 DS3/E3 LIU IC. If the user forces this signal to
toggle "High", then the LIU will transmit an "All Ones" pattern onto the line. Conversely, if the user commands
this output signal to toggle "Low" then the LIU IC will proceed to transmit data based upon the pattern that it
receives via the TxPOS[n] and TxNEG[n] output pins (of the Framer IC).
Writing a "1" to this bit-field will cause the TAOS[n] output pin to toggle "High". Writing a "0" to this bit-field will
cause this output pin to toggle "Low".
N
OTE
:
If the customer is not using an Exar 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 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 DS3/E3 LIU IC. If the user forces this
signal to toggle "High", then the internal B3ZS/HDB3 encoder (within the LIU) will be disabled. Conversely, if
the user command this output signal to toggle "Low", then the internal B3ZS/HDB3 encoder (within the LIU) will
be enabled.
Writing a "1" to this bit-field causes the Framer to toggle the Encodis output pin "High". Writing a "0" to this bit-
field will cause the Channel to toggle this output pin "Low".
N
OTES
:
1.
The B3ZS/HDB3 encoder, within the DS3/E3 LIU, is not to be confused with the B3ZS/HDB3 encoding capability
that exists within the Transmit Section of the Framer IC.
Line Interface Drive Register (Address = 0x80)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
ILOOP
Not Used
REQB
TAOS
ENCODIS
TxLEV
RLOOP
LLOOP
R/W
RO
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0