XRT72L54 Datasheet, PDF (27/484 Pages) Exar Corporation – FOUR CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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PRELIMINARY
PIN DESCRIPTION
PIN #
PIN NAME
C3
TxLev[0]
C4
RxLOS[0]
XRT72L54
FOUR CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
TYPE
O
O
DESCRIPTION
Transmit Line Build-Out Enable/Disable Select Output (to be con-
nected to the XRT7300 DS3/E3 Line Interface Unit IC):
This output pin is intended to be connected to the TxLev input pin of the
XRT7300 DS3/E3 Line Interface Unit IC. The user can control the state
of this output pin by writing a "0" or a "1" to Bit 2 (TxLev) within the Line
Interface Driver Register (Address = 0x80).
Writing a "1" to Bit 2 of the Line Interface Drive Register (Address =
0x80) will cause this output pin to toggle "high". Writing a "0" to this bit-
field will cause this output pin to toggle "low".
For DS3 Application:
If the user commands this signal to toggle "high" then the "Transmit Line
Build-Out" circuit (within the XRT7300 device) will be disabled. In this
mode, the XRT7300 device will output unshaped (e.g., square) pulses
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" circuit (within the XRT7300 device) will be dis-
abled. In this mode, the XRT7300 device will output shaped (e.g., more
rounded) pulses onto the line (via the TTIP and TRING output pins).
In order to comply with the "DSX-3 Isolated Pulse Template Require-
ment" (per Bellcore GR-499-CORE), the user is advised to command
this output pin to be "high" if the cable length (between the transmit out-
put of the XRT7300 device and the DSX-3 Cross-Connect System) is
greater than 225 feet. Conversely, the user is advised to command this
output pin to be "low" if the cable length (between the transmit output of
the XRT7300 device and the DSX-3Cross Connect System) is less than
225 feet.
For E3 Applications:
This pin can be used as a General Purpose Output pin. The Transmit
Line Build-Out circuitry (within the XRT7300 device) is not active for E3
applications.
NOTE: If the customer is not using the XRT7300 DS3/E3 Line Interface
Unit IC, then he/she can use this output pin for a variety of other pur-
poses.
Receive Section - Loss of Signal Output Indicator:
This pin is asserted when the Receive Section encounters a string of
180 consecutive 0's (for DS3 operation) or 32 consecutive 0's (for E3
operation) via the RxPOS and RxNEG pins.
This pin will be negated once the Receive Section has detected at least
60 pulses within 180 bit-periods (for DS3 operation); or the Receive
Section has detected a string of 32 consecutive bits, that does not con-
tain a string of 4 consecutive "0s" (for E3 operation).
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