XRT73L00A Datasheet, PDF (36/53 Pages) Exar Corporation – E3/DS3/STS-1 LINE INTERFACE UNIT

XRT73L00A
E3/DS3/STS-1 LINE INTERFACE UNIT
REV. 2.0.1
áç
Encoder/Decoder, write a “1” into the ENDECDIS bit-
field.
COMMAND REGISTER CR2 (ADDRESS = 0X02)
D4
D3
D2
D1
D0
Reserved ENDECDIS ALOSDIS DLOSDIS REQDIS
X
0
X
X
X
3.6 LOS DECLARATION/CLEARANCE
The XRT73L00A contains circuitry that monitors the
following two parameters associated with the incom-
ing line signals.
1. The amplitude of the incoming line signal via the
RTIP and RRING inputs; and
2. The number of pulses detected in the incoming
line signal within a certain amount of time.
If the XRT73L00A determines that the incoming line
signal is missing due to insufficient amplitude or a
lack of pulses in the incoming line signal) then it de-
clares a Loss of Signal (LOS) condition. The
XRT73L00A declares the LOS condition by toggling
the RLOS output pin “High” and by setting the RLOS
bit field in Command Register 0 to “1”.
If the XRT73L00A determines that the incoming line
signal has been restored (e.g., there is sufficient am-
plitude and pulses in the incoming line signal) then it
clears the LOS condition by toggling the RLOS output
pin “Low” and setting the RLOS bit-field to “0”.
The LOS Declaration/Clearance scheme that is em-
ployed in the XRT73L00A is based upon ITU-T Rec-
ommendation G.775 for both E3 and DS3 applica-
tions. The LOS Declaration and Clearance criteria
that the XRT73L00A uses for each of these modes
(e.g., E3 and DS3) are presented below.
3.6.1 The LOS Declaration/Clearance Criteria
for E3 Applications
When the XRT73L00A is operating in the E3 Mode, it
declares an LOS Condition if the signal amplitude
drops to -35dB or below. The XRT73L00A clears the
LOS Condition if the signal amplitude rises back up to
-15dB or above. Figure 22 illustrates the signal levels
at which the XRT73L00A asserts and clears LOS.
FIGURE 22. THE SIGNAL LEVELS THAT THE XRT73L00A DECLARES AND CLEARS LOS (E3 MODE ONLY)
0 dB
-12 dB
-15dB
LOS Signal Must be Cleared
Maximum Cable Loss for E3
-35dB
LOS Signal may be Cleared or Declared
LOS Signal Must be Declared
Timing Requirements associated with Declaring
and Clearing the LOS Indicator for E3 Applica-
tions
The XRT73L00A was designed to meet the ITU-T
G.775 specification timing requirements for declaring
and clearing the LOS indicator. The XRT73L00A de-
clares an LOS between 10 and 255 UI or E3 bit-peri-
ods after the actual time the LOS condition oc-
curred. The XRT73L00A clears the LOS indicator
within 10 to 255 UI after restoration of the incoming
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