ACS8530 datasheet(29/152 Pages) SEMTECH

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ADVANCED COMMUNICATIONS

FINAL

DATASHEET

Revision 3.02/November 2005 © Semtech Corp.

Page 29

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ACS8530 SETS

Bits [3:0], or changed via the T4 priority (Reg. 18 to 1E,

when Reg. 4B, Bit 4 = 1).

Consequently the phase detector from the T4 DPLL could

be used to measure the phase difference between the

currently selected source and the stand-by source, or it

could be used to measure the phase wander of all stand-

by sources with respect to the current source by selecting

each input in sequence. An MTIE and TDEV calculation

could be made for each input via external processing.

Configuration for Redundancy Protection

When two ACS8530 devices are to be used in a

redundancy-protection scheme within a Network Element

(NE), one will be designated as Master, one as Slave.

It is expected that an NE will use the T0 output for its

internal operations. The phase of the outputs from the T4

path (TO8 & TO9) will not be aligned, unless the T4

outputs are locked to the T0 outputs.

In many applications, the clocks supplied into the system

are required to be aligned not only in frequency, but also

in phase between the Master and Slave devices. This

ensures minimal disturbance when any clock sink

switches between Master and Slave.

In order to ensure that the outputs of the two ACS8530s

are always aligned in frequency and phase, the

procedures in Table 10 should be followed.

In order to maintain the conditions outlined in Table 10 it

is necessary for software systems to maintain monitoring

and control functions. These monitoring functions should

either poll the device or respond to interrupts in order to

maintain the correct settings within the two devices.

Please refer to the descriptions or registers mentioned in

Table 10 and also Regs 34, 3B, 48, 67 and 69, for more

details on these associated settings. See also Application

Note AN-SETS-7.

Table 10 How to Align the Outputs of Two ACS8530s

Action

Result

If possible, one device (the

nominated Slave) should lock to

the other device (the nominated

Master).

With the Slave locked to the

Master, their output frequencies

will be guaranteed to be the

same.

All programmed priorities within

the two devices should be the

same, except for the fact that:

(1) the Master output is

designated the highest priority

input on the Slave,

(2) the Slave output is

designated zero priority

(disabled) on the Master (Reg. 18

to 1E).

These two actions ensure that if

the Master device fails, the Slave

device will switch to lock to the

same source that the Master was

locked to before it failed.

Any input detected as invalid in

one device should be disabled

within the other device

(Reg. 0E/0F & 30/31).

Phase Build-out should be

disabled on the Slave whilst it is

locked to the Master.

This will ensure that the phase of

the Slave is locked to the phase

of the Master. It also enables the

use of the Phase offset control

between the Master and Slave.

Revertive mode should be

enabled.

This will ensure that the Slave

locks to the Master although it

may have been locked to another

source previously.

The bandwidth of the Slave

should be set higher than that of

the Master (it is recommended to

configure the slave with the

highest supported bandwidth).

This ensures that any transient

occurring on the output of the

Master is followed as closely as

possible on the Slave.

Table 11 MSTSLVB Pin Operation

MSTSLVB

Feature

Setting

Reason

1 =

Master

Priority of

input I11

As programmed

(program 0 to

ensure it gets

disabled)

Make sure that the

designated Master

device cannot lock to

the output of the

Slave device.

Phase

Build-out

As programmed in

If the system

requires PBO, then

this being enabled

on the Master will

give the overall

system performance

with PBO. The slave

only needs to track

the Master (no PBO).

Revertive

mode

As programmed in

Revertive behavior of

the Master in a

Master/Slave

system will define

the overall Revertive

behavior of the

system.

T0 DPLL

bandwidth

As programmed in

or manual)

Device selects

locked or acquisition

bandwidth.

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