XRT75R12 Datasheet, PDF (25/89 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR

PRELIMINARY
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR
XRT75R12
REV. P1.0.2
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 2.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 2: THE ALOS (ANALOG LOS) DECLARATION AND CLEARANCE THRESHOLDS FOR A GIVEN SETTING OF
LOSTHR AND REQEN (DS3 AND STS-1 APPLICATIONS)
APPLICATION
REQEN SETTING
LOSTHR SETTING
SIGNAL LEVEL TO DECLARE ALOS
DEFECT
SIGNAL LEVEL TO CLEAR ALOS
DEFECT
DS3
0
0
< 75mVpk
> 130mVpk
1
0
< 45mVpk
> 60mVpk
0
1
< 120mVpk
> 45mVpk
1
1
< 55mVpk
> 180mVpk
STS-1
0
0
< 120mVpk
> 170mVpk
1
0
< 50mVpk
> 75mVpk
0
1
< 125mVpk
> 205mVpk
1
1
< 55mVpk
> 90mVpk
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.
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