XRT72L56 Datasheet, PDF (162/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L56 SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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PRELIMINARY
POSn”, “RxNEGn” and “RxLineClk_n” signals will be
routed directly to the “TxPOSn”, “TxNEGn” and
“TxLineClk_n” signals.
Setting this bit-field to “1” configures the channel to
operate in the “Remote Loop-Back” Mode.
Bit 5 - REQB - (Receive Equalization Enable/Dis-
able Select)
This Read/Write bit-field allows the user to control the
state of the REQB output pin of the Framer device.
This output pin is intended to be connected to the
REQB input pin of the XRT7300 DS3/E3/STS-1 LIU
IC. If the user forces this signal to toggle "High”, then
the internal Receive Equalizer (within the XRT7300
device) will be disabled. Conversely, if the user forces
this signal to toggle "Low”, then the Receive Equalizer
(within the XRT7300 device) will be enabled.
The purpose of the internal Receive Equalizer (within
the XRT7300 device) is to compensate for the Fre-
quency-Dependent attenuation (e.g., cable loss), that
a line signal will experience as it travels through coax-
ial cable, from the transmitting to the receiving termi-
nal.
Writing a “1” to this bit-field causes the Framer device
to toggle the REQB output pin "High”. Writing a “0” to
this bit-field causes the Framer device to toggle the
REQB output pin "Low”.
For information on the criteria that should be used
when deciding whether to enable or disable the Re-
ceive Equalizer, 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 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 device.
This output pin is intended to be connected to the
TAOS input pin of the XRT7300 DS3/E3/STS-1 LIU
IC. if the user forces this signal to toggle "High”, then
the XRT7300 device will transmit an “All Ones” pat-
tern onto the line. Conversely, if the user commands
this output signal to toggle "Low” then the XRT7300
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 XRT7300 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 de-
vice. This output pin is intended to be connected to
the ENCODIS input pin of the XRT7300 DS3/E3/
STS-1 LIU IC. If the user forces this signal to toggle
"High”, then the internal B3ZS/HDB3 encoder (within
the XRT7300 device) will be disabled. Conversely, if
the user commands this output signal to toggle "Low”,
then the internal B3ZS/HDB3 encoder (within the
XRT7300 device) 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 XRT7300
device 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 XRT7300 IC) if the Transmit
and Receive DS3/E3 Framer (within the
XRT72L56) are 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 this bit-field and the Encodis
output pin can be used for other purposes.
4. It is permissible to tie both the ENCODIS and
DECODIS input pins (of the XRT7300 device) to
the Encodis output pin of the XRT72L56 DS3/E3
Framer IC.
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 device.
This output pin is intended to be connected to the Tx-
LEV input pin of the XRT7300 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”.
If the user commands this signal to toggle "High”,
then the Transmit Line Build-Out circuitry, within the
XRT7300 device will be disabled. In this mode, the
XRT7300 LIU IC will generate unshaped (e.g.,
square) pulses out onto the line, via the TTIP and
TRING output pins.
Conversely, if the user commands this signal to toggle
"Low”, then the Transmit Line Build-Out circuitry, with-
in the XRT7300 device will be enabled. In this mode,
the XRT7300 device will generate shaped pulses on-
to the line, via the TTIP and TRING output pins.
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