ACS8515REV2.1 Semtech Corporation, ACS8515REV2.1 Datasheet - Page 32

• Manufacturer Part Number: ACS8515REV2.1
• Description: Line Card Protection Switch for Sonet or SDH Network Elements
• Manufacturer: Semtech Corporation

Modes of Operation
Modes of Operation
Free-run Mode
Free-run Mode
disqualified for phase, frequency, inactivity or if
the source is outside the DPLL lock range. If
the currently selected reference source is
disqualified, the next highest priority, active
reference source is selected.
Restoration of repaired reference sources is
handled carefully to avoid inadvertant disruption
of the output clock. The ACS8515 operates in
a Non-Revertive mode by default. In this mode,
if the restored reference source has a higher
priority than the reference source which is
currently selected, a switch-over to the restored
source will not tale place automatically. A
restored reference source will assume its
correct place in the priority table but a switch-
over will only take place automatically upon
failure of the currently selected source. It is
possible to invoke a switch-over by external
control or by enabling Revertive mode.
Modes of Operation
Modes of Operation
Modes of Operation
The ACS8515 has three primary modes of
operation (Free-run, Locked and Holdover)
supported by three secondary, temporary
modes (Pre-Locked, Lost_Phase and Pre-
Locked2). These are shown in the State
Transition Diagram, Figure 10.
The ACS8515 can operate in Forced or
Automatic control. On reset, the ACS8515
reverts to Automatic Control, where transitions
between states are controlled completely
automatically. Forced Control can be invoked
by configuration, allowing transitions to be
performed under external control. This is not
the normal mode of operation, but is provided
for special occasions such as testing, or where
a high degree of hands-on control is required.
Free-run Mode
Free-run Mode
Free-run Mode
The Free-run mode is typically used following a
power-on-reset or a device reset before
network synchronization has been achieved. In
Revision 2.01/December 2005 Semtech Corp.
ADVANCED COMMUNICATIONS
32
the
synchronization signals generated from the
ACS8515 are based on the Master clock
frequency provided from the external oscillator
and are not synchronized to an input reference
source. The frequency of the output clock is a
fixed multiple of the frequency of the external
oscillator, and the accuracy of the output clock
is equal to the accuracy of the Master clock.
The transition from Free-run to Pre-locked
occurs when the ACS8515 selects a reference
source.
Pre-Locked Mode
Pre-Locked Mode
Pre-Locked Mode
Pre-Locked Mode
Pre-Locked Mode
The ACS8515 will enter the Locked state in a
maximum of 100 seconds, as defined by GR-
1244-CORE specification, if the selected
reference source is of good quality. If the device
cannot achieve lock within 100 seconds, it
reverts to Free-run mode and another reference
source is selected.
Locked Mode
Locked Mode
Locked Mode
Locked Mode
Locked Mode
The Locked mode is used when an input
reference source has been selected and the
PLL has had time to lock. When the Locked
mode is achieved, the output signal is in phase
and locked to the selected input reference
source. The selected input reference source is
determined by the priority table. When the
ACS8515 is in Locked mode, the output
frequency and phase follows that of the
selected input reference source. Variations of
the external crystal frequency have a minimal
effect on the output frequency.
minimum to maximum frequency range is
affected. Note that the term, 'in phase', is not
applied in the conventional sense when the
ACS8515 is used as a frequency translator (e.g.,
when the input frequency is 2.048 MHz and
the output frequency is 19.44 MHz) as the input
and output cycles will be constantly moving past
each other; however, this variation will itself be
cyclical over time unless the input and output
are not locked.
ACS8515 Rev2.1 LC/P
Free-run
mode,
the
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