ACS8510REV2.1 Semtech Corporation, ACS8510REV2.1 Datasheet - Page 41

• Manufacturer Part Number: ACS8510REV2.1
• Description: Synchronous Equipment Timing Source for Sonet or SDH Network Elements
• Manufacturer: Semtech Corporation

Modes of Operation
Modes of Operation
Free-run mode
Free-run mode
Pre-Locked mode
Pre-Locked mode
Modes of Operation
Modes of Operation
Modes of Operation
The ACS8510 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 11.
The ACS8510 can operate in Forced or
Automatic control. On reset, the ACS8510
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
the
synchronization signals generated from the
ACS8510 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 ACS8510 selects a reference
source.
Pre-Locked mode
Pre-Locked mode
Pre-Locked mode
The ACS8510 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.
device cannot achieve lock within 100 seconds,
it reverts to Free-run mode and another
reference source is selected.
Revision 2.00/September 2003
ADVANCED COMMUNICATIONS
Free-run
mode,
Semtech Corp.
the
timing
If the
and
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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
ACS8510 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
ACS8510 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.
Lost_Phase mode
Lost_Phase mode
Lost_Phase mode
Lost_Phase mode
Lost_Phase mode
Lost-phase mode is entered when the current
phase error, as measured within the DPLL, is
larger than a preset limit (see register 04, bits
5:3), as a result of a frequency or phase
transient on the selected reference source.
This mode is similar in behavior to the Pre-locked
or Pre-locked(2) modes, although in this mode
the DPLL is attempting to regain lock to the same
reference rather than attempt lock to a new
reference.
If the DPLL cannot regain lock within 100 s, the
source is disqualified, and one of the following
transitions takes place:
1. Go to Pre-Locked(2);
2. Go to Holdover;
- If a known-good standby source is available.
- If no standby sources are available.
ACS8510 Rev2.1 SETS
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