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XRT79L71
PRELIMINARY
361
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The Clock and Data Recovery block (now having no incoming E3 line signal to lock onto) will begin to drift
towards its VCO center frequency. As the Clock and Data Recovery block begins to do this, at some point,
the "Recovered Clock" frequency (of the Clock and Data Recovery) will drift to beyond the point where it
differs from the Reference Clock signal (being supplied by the "SFM Synthesizer" block) by 0.5% (or
5000ppm). Once the "Recovered Clock" signal differs from the "Reference Clock" signal by 5000ppm, or
more, then it will declare the LOL Defect Condition.
Once the Clock and Data Recovery block has declared the LOL Defect condition, it will now "lock" onto the
"Reference Clock" signal (from the SFM Synthesizer block). In this case, the "Recovered" clock signal (from
the Clock and Data Recovery block) will be derived from the "Reference Clock" signal (from the "SFM
Synthesizer" block).
For the duration that the AGC Block is in the "High-Gain" Mode (which indicates that no signal energy is
presented at the RTIP/RRING input pins), then the Clock and Data Recovery block will remain in the "above-
mentioned" state. In other words, it will continue to declare the LOL Defect Condition. It will also continue to
synthesize and route a 34.368MHz clock signal (to the down-stream circuitry, such as the Receive DS3/E3
Framer block) based upon the "Reference Clock" signal from the "SFM Synthesizer" block.
If "A Signal" is present at the RTIP/RRING Input Pins
If there is an impairment, within the incoming E3 line signal, such that signal energy was still present at the
RTIP/RRING input pins, however "Recovered Clock" frequency (from the Clock and Data Recovery) differs
from the "Reference Clock" Frequency by more than 5000ppm; then all of the following will happen.
The Receive DS3/E3 LIU Block may (or may not) declare the LOS Defect condition (please see SEE”THE information on how the Receive DS3/E3 LIU Block declares the LOS Defect Condition). This condition
depends upon the amplitude of the signal being applied to the RTIP/RRING input pins.
The Clock and Data Recovery block (now locking onto a signal that is more than 5000ppm off in frequency,
from the "Reference Clock" signal (being supplied by the "SFM Synthesizer" block). As a consequence, the
Clock and Data Recovery will declare the LOL Defect Condition.
Once the Clock and Data Recovery block has declared the LOL Defect condition, it will now "lock" onto the
"Reference Clock" signal (from the SFM Synthesizer block). In this case, the "Recovered" clock signal (from
the Clock and Data Recovery block) will be derived from the "Reference Clock" signal (from the "SFM
Synthesizer" block).
In this case, the AGC Block will not be in the "High-Gain" Mode (which indicates that there is some signal
energy present at the RTIP/RRING input pins). Whenever this is the case, then the Clock and Data Recovery
block will constantly be cycling through the following states.
STATE 1: The Clock and Data Recovery is locked onto a "line" signal that is more than 5000ppm off in
frequency from the "Reference Clock" signal (that is supplied by the SFM Synthesizer block).
As a
consequence, the Clock and Data Recovery declares the LOL Defect Condition.
STATE 2: Now that the Clock and Data Recovery is declaring the LOL Defect condition, it (for the time-being)
will cease to attempt to lock onto the incoming line signal (via the RTIP/RRING input pins), and will (instead)
lock onto the "Reference Clock" signal (that originates from the SFM Synthesizer block). In this case, the
difference between "Recovered" Clock and the "Reference Clock" is no longer be greater than 5000ppm. It will
now be 0ppm (because the "Recovered" Clock is now being synthesized from the "Reference Clock"). As a
consequence, the Clock and Data Recovery will now clear the LOL Defect condition.
STATE 3: Now that the Clock and Data Recovery has cleared the LOL Defect condition, it will now attempt to
acquire lock with the incoming E3 line signal. As the Clock and Data Recovery does this, it will continue to
make the comparison between the frequency of its "Recovered" Clock and the frequency of the "Reference
Clock".
5.3.1.5
The SFM (Single-Frequency Mode) Synthesizer Block