STC5455 datasheet(20/56 Pages) CONNOR-WINFIELD

20 / 56 page

Page 20 of 56 TM121 Rev: P1.3

Date: October 24, 2011

STC5455

Synchronous Clock for SETS

Functional Specification

Data sheet

Preliminary

External SYNC Inputs and Refer-

ence Inputs Details

The STC5455 accepts 5 external reference inputs.

The reference inputs may be selected to accept either

the auto-detect acceptable reference frequency which

can be automatically detected or manually acceptable

reference frequency. Reference inputs REF4 and

REF5 are LVPECL/LVDS and the remaining three are

LVCMOS. All 5 reference inputs are monitored contin-

uously for frequency, activity and quality. Each timing

generator may select any of the reference inputs

when the device is in external timing mode. T4 may

accept T0’s output as its input via internal feedback

path.

External Frame Sync Inputs

The STC5455 has three external frame sync inputs at

2kHz or 8kHz on the pin EX_SYNC1, EX_SYNC2,

and EX_SYNC3 respectively. The frequency of the

external frame sync inputs are auto-detecting.

To achieve frame alignment, any one of the three

external frame sync inputs may be selected as frame

reference for T0 selected REF1 to REF5 individually

at the register Frame Phase Align. Sampling edge of

the external sync inputs can be configured as falling

or rising at the register EX SYNC Edge Config

Acceptable Frequency and Frequency Offset

Detection

The STC5455 can automatically detect the frequency

of the reference input when the user enable the auto-

detection function at the register Ref Acceptable

Freq. The acceptable auto-detect frequencies are:

8kHz, 64kHz, 1.544MHz, 2.048MHz, 19.44MHz,

38.88MHz,

77.76MHz,

6.48MHz,

8.192MHz,

16.384MHz, 25MHz, 50MHz or 125MHz. These fre-

quencies can be detected automatically in the detec-

tor. The detector operates continuously to detect the

frequency of reference inputs. Any carrier frequency

change will be detected within 1ms. Each input is also

monitored for frequency offset between input and the

internal freerun clock. The frequency offset is a key

factor to determine qualification of the reference

inputs. See register Ref Index Selector and Ref Info.

STC5455 provides another option which allows the

user to select the manually acceptable reference fre-

quency for all the reference inputs, at the integer mul-

tiple of 8kHz (Nx8kHz, N is integer from 1 to 32767).

Hence the manually acceptable reference frequency

range is integer multiple of 8kHz from 8kHz to

262.136MHz. When a manually acceptable reference

frequency is used, the user need to access the regis-

ter Ref Index Selector and Ref Acceptable Freq.

Each input is monitored for frequency offset between

input and the internal freerun clock. The frequency

offset is shown in the register Ref Info when associ-

ate reference index is selected at the register Ref

Index Selector.

Activity Monitoring

Activity monitoring is also a continuous process which

is used to identify if the reference input is in normal. It

is accomplished with a leaky bucket accumulation

algorithm, as shown in Figure 2. The “leaky bucket”

accumulator has a fill observation window that may

be set from 1 to 16ms, where any hit of signal abnor-

mality (or multiple hits) during the window increments

the bucket count by one. The leak observation win-

dow is 1 to 16 times the fill observation window. The

leaky bucket accumulator decrements by one for

each leak observation window that passes with no

signal abnormality. Both windows operate in a con-

secutive, non-overlapping manner. The bucket accu-

mulator has alarm assert and alarm de-assert

thresholds that can each be programmed from 1 to

64.

Figure 2: Activity Monitor

Applications can write to the following registers to

configure the activity monitor: Fill Obs Window,

Leak Obs Window, Bucket Size, Assert Threshold,

and De Assert Threshold.

Setting the bucket size to 0 will bypass the leak

bucket accumulator and assert or de-assert the activ-

ity alarm based on results of frequency detector and

pulse monitor only. A non-zero bucket size must be

greater than or equal to the alarm assert threshold

Leaky

Bucket

Accumulator

Leak Observation

Window, 1~16 x Fill

Observation Window

Fill Observa-

tion Window,

1ms ~ 16ms

Pulse

Monitor

Ref

Alarm Assert

Alarm De-Assert

Frequency

Detector

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