zl30462 Zarlink Semiconductor, zl30462 Datasheet - Page 10

• Manufacturer Part Number: zl30462
• Description: Vibratto-s Dvd Processor Product Brief
• Manufacturer: Zarlink Semiconductor

1.6.2
The Free-run state is entered when synchronization to the network is not required or is not possible. Typically this
occurs during installation, repairs or when a Network Element operates as a master node in an isolated network. In
the Free-run state, the accuracy of the generated clocks is determined by the accuracy and stability of the ZL30462
Master Crystal Oscillator. When powering up the equipment, it is recommended that the module has at least 2
hours to stabilize after the equipment has reached its normal operating temperature.
1.6.3
The Normal State is entered when Normal mode is selected and a good quality reference clock is available. The
ZL30462 automatically detects the frequency of the reference clock (8 kHz, 1.544 MHz, 2.048 MHz or 19.44 MHz)
and sets the LOCK status pin to logic 1 after acquiring synchronization. In the Normal state all generated clocks
(C2o, C8o, C16o, JA19Mo, JA155P/N-1 and JA155P/N-2) and frame pulse (F16o) are derived from network timing.
To guarantee uninterrupted synchronization, the ZL30462 continuously monitors the quality of both input reference
clocks. This dual architecture enables quick replacement of a poor or failed reference and minimizes the time spent
in other states.
During this state the ZL30462 can tolerate a 17 ppm/s frequency change (on the active input) without generating an
alarm or changing state.
1.6.4
The Holdover State is typically entered for short durations while network synchronization is temporarily disrupted. In
Holdover Mode, the ZL30462 generated clocks are not locked to an external reference signal, but these outputs are
based on stored coefficients in memory. These coefficients are determined while the module is in Normal State for
at least 10 minute after the modules stabilization period.”
The initial frequency offset of the ZL30462’s DPLL in Holdover Mode is ±1x10
transitioned into Holdover Mode, holdover stability is determined by the stability of the 20 MHz Master Clock
Oscillator (OSC pin), which is a ±20 ppm crystal oscillator.
1.6.5
The Auto Holdover state is a transitional state that the ZL30462 enters automatically when the active reference fails
unexpectedly. When the ZL30462 detects loss of reference it waits in Auto Holdover state until the failed reference
recovers. The HOLDOVER status pin may be used to alert the system controller about the failure and in response
the controller may switch to the secondary reference clock. The HOLDOVER pin indicates when you are in either
Auto Holdover and Holdover states.
If the selected input fails (or becomes invalid for any reason) the ZL30462 will transition into Auto-Holdover. If the
system controller then elects to switch to the other input and that input is also invalid, then the ZL30462 will remain
in Auto Holdover until that input becomes valid. This is an internal protection system, to ensure that the module
does not use an invalid reference.
If the ZL30462 is reset at any time (e.g., during power-up) and mode select pins are trying to force the module to
lock to an invalid input (MS1, MS2 == 00) the module will transition into Auto Holdover and the HOLDOVER pin will
be asserted. Because the reset function clears the ZL30462’s memory, then there will be no holdover history. In this
case, even though the output status pin is showing that the module is in Holdover, the output clock accuracy will
default to that of Freerun mode.
So to summarise the above,
mode (MS2, MS1 == 00) generating synchronous clocks. The State Machine is designed to perform some
transitions automatically, leaving other, less time dependent tasks to the system controller. The state machine
includes two stimulus signals which are critical to automatic operation: “OK --> FAIL” and “FAIL --> OK” that
represent loss (and recovery) of the reference signal or its drift by more than ±30000 ppm. Their transitions force
Free-Run State
Normal State (Locked State)
Holdover State
Auto Holdover State
i
n a typical Network Element application, the ZL30462 will typically operate in Normal
Zarlink Semiconductor Inc.
ZL30462
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. Once the ZL30462 has
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