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XRT79L71
PRELIMINARY
359
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
For the duration that the Clock and Data Recovery block is maintaining "lock" with the incoming E3 line signal,
then all of the following will be true.
The Clock and Data Recovery block will be synthesizing a 34.368MHz "recovered" clock signal that is
derived from the incoming E3 line signal.
The Clock and Data Recovery block will route this 34.368MHz clock signal to all down-stream circuitry (e.g.,
the Receive DS3/E3 Framer block, etc.). Each of these down-stream blocks will use this 34.368MHz clock
signal as their timing source.
The Clock and Data Recovery block will be continuously comparing the frequency of its Recovered Clock
signal with a "Reference" Clock signal that it receives from the "SFM Synthesizer" Block. As long as the
differences between these two frequencies is less than 0.5% (or 5000ppm), then the Clock and Data
Recovery block will continue to operate in this "normal" mode.
NOTE: Information on the "SFM Synthesizer" block can be found in Section 4.3.1.5. The LOL (Loss of Lock) Defect Declaration Criteria
As mentioned above, the Clock and Data Recovery block will be continuously monitoring the frequency of its
recovered clock signal with a "Reference" Clock signal that it receives from the "SFM Synthesizer" block. As
long as the differences between these two frequencies is less than 0.5% (or 5000ppm), then the Clock and
Data Recovery block will continue to operate in this "normal" mode.
However, if the difference between these two frequencies exceeds 0.5% (or 5000ppm), then the Clock and
Data Recovery block will declare the "LOL (Loss of Lock) Defect Condition". Whenever the Clock and Data
Recovery block declares the "Loss of Lock Defect Condition", then it will cease its attempt to acquire and
maintain "phase-lock" with the incoming E3 line signal. Instead, the Clock and Data Recovery will now lock
onto the reference clock signal from the "SFM Synthesizer" block. The Clock and Data Recovery will make this
transition, in order to guarantee that all "down-stream" circuitry (e.g., the Receive DS3/E3 Framer block) will be
provided with a proper line-rate clock signal.
The XRT79L71 will inform the user that it is declaring the "Loss of Lock Condition" by doing all of the following.
It will set Bit 2 (Receive LOL Defect Declared), within the "LIU Alarm Status" Register, to "1" as depicted
below.
LIU Interrupt Status Register (Address = 0x1302)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
Change of
FL
Condition
Interrupt
Status
Change of
LOL
Condition
Interrupt
Status
Change of
LOS
Condition
Interrupt
Status
Change of
DMO
Condition
Interrupt
Status
R/O
RUR
0
1
0