STC5428 Datasheet, PDF(27/66 Page) Connor-Winfield Corporation

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STC5428 Datasheet, PDF (27/66 Pages) Connor-Winfield Corporation – Synchronous Clock for SETS

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STC5428

Synchronous Clock for SETS

DATASHEET

the auto reference elector always work in this mecha-

nism. The detail description of the reference selection

mode is in following sections.

The reference priority is indicated in the reference pri-

ority table which is shown in register Ref 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. â0â revokes the reference from the

election, while 1 to 15 set the priority, where â1â has

the highest, and â15â has the lowest priority. The high-

est priority pre-qualified reference then is a candidate

selected by the automatic reference elector. If multi-

ple references share the same priority, the one that

has been qualified for the longest time will be recom-

mended to be the candidate. If the current highest pri-

ority reference input fails, the next highest priority

reference is selected as the candidate.

FuncEtleicot nal Specification

Candidate

Reference

Candidate

Reference

Available

Candidate

Reference

Available

No Candidate

Reference

Available and

HO not Available

Elect

Holdover

No Candidate

Reference

Available and

HO is Available

Elect

Freerun

Figure 4: Automatic Reference Elector States

In order to avoid disturbance of the clock output, the

candidate reference selected 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

ârevertiveâ bit of the Control Mode to â1â for revertive

or to â0â for non-revertive operation.

In revertive mode, the automatic reference elector will

pre-empted the current candidate reference if the

new recommended candidate reference has higher

priority.

In non-revertive mode, the current candidate refer-

ence will not be pre-empted by any new candidate

until it is disqualified.

If there is no candidate reference available, freerun or

holdover will be recommended by the automatic ref-

erence elector depending on the holdover history

availability.

Automatic Reference Selection

The T0 and T4 timing generators may be individually

operated automatic reference input selection mode.

The mode is selected via the Control Mode registers.

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 Auto

Elect Ref registers.

Manual Reference Selection Mode

In manual reference selection mode, the user may

select the reference manually. This mode is selected

via the Control Mode registers. The reference is

selected by writing to the Manual Select Ref regis-

ters. The user may also has the device enter freerun

or holdover manually by writing to the Manual Select

Ref registers. Besides, T4 may select T0âs output as

the selected reference.

Figure 4 shows the operation states for automatic ref-

erence elector.

Hard-wired Manual Reference Selection

Besides the manual reference selection mode, the

STC5428 provides a special mode to switch between

two pre-selected reference directly from a dedicated

pin SRCSW. The two pre-selected references are

configured at the register Hard Wired Switch Pre

Selection. It can make the device enter the freerun or

holdover by writing to the register Hard Wired Switch

Pre Selection. In this mode, the pin SRCSW oper-

ates as a simple switch by setting high or low. Hard-

Page 27 of 66

Preliminary

Rev: 0.2

Date: April 3, 2014

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