Digital To Analog Converter - Avaya Nortel Communication Server 1000 Reference

To prevent chatter due to repeated automatic switching between primary and secondary
reference sources, a time-out mechanism of at least 10 seconds is implemented.

Digital to analog converter

The Digital to Analog Converter (DAC) enables the microprocessor to track, hold, and modify
the error signal generated in the digital PLL.
The firmware uses the available memory on the clock controller to provide error-burst detection
and correction. Temporary holdover occurs in the momentary absence of the reference
clock.
Holdover and free-run
In the temporary absence of a synchronization reference signal, or when sudden changes
occur on the incoming reference due to error bursts, the clock controller provides a stable
holdover. Free-run mode is initiated when the clock controller has no record of the quality of
the incoming reference clock.
If the command "free run" is given, the clock controller enters the free-run mode and remains
there until a new command is received. Free-run automatically initiates after the clock controller
is enabled.
Signal conditioning
Drivers and buffers are provided for all outgoing and incoming lines.
Sanity timer
The sanity timer resets the microprocessor in the event of system hang-up.
Microprocessor
The microprocessor does the following:
• communicates with software
• monitors two references
• provides a self-test during initialization
• minimizes the propagation of impairments on the system clock due to errors on the
primary or secondary reference clocks
Circuit Card Reference
Functional description
July 2011 591