XRT75R12D_07 Datasheet, PDF (27/133 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET

XRT75R12D
REV. 1.0.3 TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
3.5 LOS (Loss of Signal) Detector
3.5.1 DS3/STS-1 LOS Condition
A Digital Loss of SIgnal (DLOS) condition occurs when a string of 175 ± 75 consecutive zeros occur on the line.
When the DLOS condition occurs, the DLOS_n bit is set to “1” in the status control register. DLOS condition is
cleared when the detected average pulse density is greater than 33% for 175 ± 75 pulses. Analog Loss of
Signal (ALOS) condition occurs when the amplitude of the incoming line signal is below the threshold as shown
in the Table 3.The status of the ALOS condition is reflected in the ALOS_n status control register. RLOS is the
logical OR of the DLOS and ALOS states. When the RLOS condition occurs the RLOS_n output pin is toggled
“High” and the RLOS_n bit is set to “1” in the status control register.
TABLE 3: THE ALOS (ANALOG LOS) DECLARATION AND CLEARANCE THRESHOLDS FOR A GIVEN SETTING OF
REQEN (DS3 AND STS-1 APPLICATIONS)
APPLICATION REQEN SETTING
DS3
0
1
STS-1
0
1
SIGNAL LEVEL TO DECLARE ALOS SIGNAL LEVEL TO CLEAR ALOS
DEFECT
DEFECT
< 41mVpk
> 102mVpk
< 52mVpk
> 117mVpk
< 51mVpk
> 114mVpk
< 58mVpk
> 133mVpk
3.5.2 Disabling ALOS/DLOS Detection
For debugging purposes it is useful to disable the ALOS and/or DLOS detection. Writing a “1” to both
ALOSDIS_n and DLOSDIS_n bits disables the LOS detection on a per channel basis.
3.5.3 E3 LOS Condition:
If the level of incoming line signal drops below the threshold as described in the ITU-T G.775 standard, the
LOS condition is detected. Loss of signal is defined as no transitions for 10 to 255 consecutive zeros. No
transitions is defined as a signal level between 15 and 35 dB below the normal. This is illustrated in Figure 8.
The LOS condition is cleared within 10 to 255 UI after restoration of the incoming line signal. Figure 9 shows
the LOS declaration and clearance conditions.
FIGURE 8. LOSS OF SIGNAL DEFINITION FOR E3 AS PER ITU-T G.775
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
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