STC5423 datasheet(21/60 Pages) CONNOR-WINFIELD

21 / 60 page

Page 21 of 60 TM114 Rev: 1.4

Date: October 24, 2011

STC5423

Synchronous Clock for SETS

Functional Specification

Data sheet

disqualify the reference. It may then be re-qualified if

the activity alarm is off and the reference is within the

qualification range for more than the qualification

time.

The reference qualification status of each reference

may then be read from the register Ref Qual.

Figure 3: Reference Qualification Scheme

Automatic Reference Election Mechanism

The STC5423 has an auto reference elector always

elect the most appropriate candidate input from the

reference inputs according to the revertivity status,

and each reference’s priority and qualification. This

mechanism operates independent of reference selec-

tion mode. In other word, regardless what the current

reference selection mode is, the auto reference elec-

tor always work in this mechanism. The detail

description of the reference selection mode is in fol-

lowing sections.

The reference priority is indicated in the reference pri-

ority table which is shown in the register Priority

Table individually for each timing generator. Each ref-

erence has one entry in the table, which may be set to

value from 0 to 15. ‘0’ revokes the reference from the

election, while 1 to 15 set the priority, where ‘1’ has

the highest and ‘15’ has the lowest priority. The high-

est priority pre-qualified reference then is a candidate

reference input selected by the automatic reference

elector. If multiple references share the same priority,

the one that has been qualified for the longest time

will be elected. If the current highest priority reference

input fails, the next-highest priority reference is

elected.

Activity

Not Good

Activity

Good

Qualified

Activity Alarm

Asserted

Activity Alarm

Asserted

Activity Alarm

De-Asserted

Out of Disqualification Range

Within Offset Qualification

Range for more than

Qualification soaking Time

Continuously

In order to avoid disturbance of the clock output, the

candidate reference elected by automatic reference

elector should be handled in two different mode:

revertive mode and non-revertive mode. The mode is

determined by either enabling or disabling the “rever-

tive” bit of the register Control Mode to “1” for rever-

tive or to “0” for non-revertive operation.

In revertive mode, the automatic reference elector will

pre-empted the current elected reference if the new

reference has higher priority.

In non-revertive mode, the current elected reference

will not be pre-empted by any new reference until it is

disqualified.

If there is no elected reference available, freerun or

holdover will be elected by the automatic reference

elector depending on the holdover history availability.

Figure 4 shows the operation states for automatic ref-

erence elector.

Automatic Reference Selection

The T0 and T4 timing generators may be individually

operated in automatic input reference selection

mode. The mode is selected at the register Control

Mode.

In automatic reference selection mode, the selected

reference is the same reference elected by the auto-

matic reference elector. The automatically selected

reference for each PLL may be read from the register

Auto Select

Figure 4: Automatic Reference Elector States

Elect

Freerun

Elect

Holdover

Candidate

No Candidate

Reference

Candidate

Reference

Available and

Elect

HO not Available

Reference

Available

Candidate

Available

Reference

No Candidate

Reference

Available and

HO is Available

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