XRT75R03D datasheet(52/134 Pages) EXAR

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XRT75R03D

REV. 1.0.2

THREE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCRONIZER

6.3

B3ZS/HDB3 Decoder:

The decoder block takes the output from clock and data recovery block and decodes the B3ZS (for DS3 or

STS-1) or HDB3 (for E3) encoded line signal and detects any coding errors or excessive zeros in the data

stream.

Whenever the input signal violates the B3ZS or HDB3 coding sequence for bipolar violation or contains three

(for B3ZS) or four (for HDB3) or more consecutive zeros, an active “High” pulse is generated on the RLCV_n

output pins to indicate line code violation.

NOTE: In Dual-Rail mode, the decoder is bypassed.

6.4

LOS (Loss of Signal) Detector:

6.4.1

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 10.The status of the ALOS condition is reflected in the ALOS_n status control

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.

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.

6.4.2

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 level is defined to be between 15 and 35 dB below the normal level. If

the signal drops below 35 dB for 10 to 255 consecutive pulse periods, LOS condition is declared. This is

illustrated in Figure 19.

TABLE 10: 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

< 75mVpk

> 130mVpk

< 45mVpk

> 60mVpk

< 120mVpk

> 45mVpk

< 55mVpk

> 180mVpk

STS-1

< 120mVpk

> 170mVpk

< 50mVpk

> 75mVpk

< 125mVpk

> 205mVpk

< 55mVpk

> 90mVpk

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