STC5455 datasheet(19/56 Pages) CONNOR-WINFIELD

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Page 19 of 56 TM121 Rev: P1.3

Date: October 24, 2011

STC5455

Synchronous Clock for SETS

Functional Specification

Data sheet

Preliminary

Short_Term_Accu_History.

Typically,

short-term

history is used by clock synthesizer in two conditions:

First, it is used in between the transition of two differ-

ent operation modes; second, it is used if LOS occurs

when the STC5455 operates in synchronized mode

with manually reference selection.In addition, short-

term history is provided to perform failure diagnostics

and evaluations.

Long-Term History

Long-term history is an average frequency offset

between the clock output and MCLK which is filtered

internally using a weighted 3rd order low-pass filter

with the long time constant. The -3 dB filter response

point can be programmed from 0.15mHz to 1.3Hz by

writing to the register History Ramp. The history

value can be read from the register Long Term Accu

History.

Device Holdover History

Device holdover history is the history data used when

the STC5455 runs in holdover mode. It is acquired

from the long term history previously described. In

synchronized mode, when timing generators PLL has

locked to the selected reference input for over 15

minutes, the long term history is stored and further

updated as the device holdover history. If LOS or LOL

occurs, the device holdover history will stay at the lat-

est updated value until re-enter the synchronized

mode and the PLL locks to the replaced selected ref-

erence input for another 15 minutes. Set Bit

HO_Usage bit of the register Control Mode to select

using device holdover history. Its value can be read

from the register Device Holdover History.

User-Specified History

The STC5455 allows user to provide the history data

created from their own sophisticated history accumu-

lation algorithms by writing to the register User Spec-

ified History. Set bit HO_Usage of the register Con-

trol Mode to select using user specified holdover his-

tory. Its value can be read from the register User

Specified History.

Phase-Locked Loop Status Details

The register PLL Status contains the detailed status

of the PLLs, including the signal activity of the

selected reference, the synchronization status, and

the availability of the holdover histories.

SYNC bit

external-timing

mode, this

bit

indicates

the

achievement of synchronization. This bit will not be

asserted in self-timing mode.

LOS bit

In external-timing mode, this bit indicates the loss of

signal on the selected reference. This bit will not be

asserted in self-timing mode.

LOL bit

In external-timing mode, the bit will be set if the PLL

fails to achieve or maintain lock to the selected refer-

ence. This bit will not be asserted in self-timing mode.

It is also not complementary to the SYNC bit. Both

bits will not be asserted when the PLL is in the pull-in

process. The pull-in process usually occur when

switch to a new selected reference or recover from

the LOS/LOL.

OOP bit

This bit indicates that the selected reference is out of

the pull-in range. This is meaningful only if in exter-

nal-timing mode. This bit will not be asserted in self-

timing mode. The frequency offset is relative to the

digitally calibrated freerun clock.

SAP bit

This bit when set indicates that the PLL’s output

clocks have stopped following the selected reference

because the frequency offset of the selected refer-

ence is out of pull-in range (OOP). User can write to

the Control Mode register to program whether the

PLL shall follow the selected reference outside of the

specified pull-in range or just stay within the pull-in

range boundary.

FEE bit

This bit indicates whether an error occurs in the frame

edge detection process in phase align mode.

DHT bit

This bit indicates whether the device holdover history

is tracking on the current selected reference (updat-

ing by the long-term history).

HHA bit

This bit indicates the availability of the holdover his-

tory, which may be either the user provided history or

the device holdover history.

STC5455 Datasheet(PDF) 19 Page - Connor-Winfield Corporation

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