PT7A4401C Datasheet, PDF (7/27 Pages) List of Unclassifed Manufacturers – PT7A4401C T1/E1 System Synchronizer

Data Sheet
PT7A4401C T1/E1 System Synchronizer
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Table 3. Input Frequency Selection
FS2
FS1
Input Frequency
0
0
Reserved
0
1
8kHz
1
0
1.544MHz
1
1
2.048MHz
States of Operation
Typically, the PT7A4401C operates in either the Normal or
Free-Run state. However, when the input signal is temporarily
missing or its frequency is temporarily out of specification, it
operates in Auto-Holdover State (Refer to Table 7).
Normal State
In Normal State, the output signals of the PT7A4401C are
synchronized with the input reference signal by the DPLL.
Free-Run State
State Machine
If the value of MS is 1, the “Free-Run” state of operation is
forced. If the value of MS is 0, the state of operation is either
“Normal” or “Auto-Holdover”, depending upon the state of
the Input Impairment Monitor. See Table 4.
Table 4. Operation State Selection
Typically, the Free-Run State is used immediately following
system power-up before network synchronization is achieved,
or when a master clock is otherwise required.
In Free-Run State, the outputs of the PT7A4401C are
uncorrelated with the input reference signal (and the stored
information concerning the output reference signals). Instead,
these output signals are based solely on the master clock fre-
quency (OSCi).
MS
Operation State
Auto-Holdover State
0
Normal
The Auto-Holdover State will be automatically initiated when
incoming reference signal disappears or its frequency moves
outside the Auto-holdover capture range (Table 7), by either a
1
Freerun
small or large amount.
In Auto-Holdover State, the PT7A4401C output signals are
not synchronized with the external input reference signal. In-
stead, they are generated by using the information stored 30
ms to 60ms before the incoming reference signal became un-
usable.
While in Normal State, a numerical value related to the output
reference frequency is stored alternately in two memory loca-
tions every 30ms. Whenever the device is switched into Auto-
Holdover State, the value in memory between 30ms and 60ms
is used to set the output frequency of the device.
PT0108(09/02)
7
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