Meridian Nortel 1 Option 11C Technical Reference Manual page 475

If the incoming clock reference is stable, the internal clock controller will
track it, lock onto it, and match frequencies exactly. Occasionally, however,
environmental circumstances will cause the external or internal clocks to
drift. When this happens, the internal clock controller will briefly enter the
tracking stage. The green LED will flash momentarily until the clock
controller is locked onto the reference once again.
If the incoming reference is unstable, the internal clock controller will
continuously be in the tracking stage, with the LED flashing green all the
time. This condition does not present a problem, rather, it shows that the clock
controller is continually attempting to lock onto the signal. If slips are
occurring, however, it means that there is a problem with the clock controller
or the incoming line.
Free-run (non-tracking)
In free-run mode, the clock controller does not synchronize on any source, it
provides its own internal clock to the system. This mode can be used when
the Option 11C is used as a master clock source for other systems in the
network. Free-run mode is undesirable if the Option 11C is intended to be a
slave. It can occur, however, when both the primary and secondary clock
sources are lost due to hardware faults or when invoked by using software
commands.
Clock controller functions and features
The NTAK10 2MB DTI clock controller functions and features include:
• phase-locking to a reference, generating the 10.24 Mhz system clock,
and distributing it to the CPU through the backplane. Up to two
references at a time may be accepted.
• providing primary to secondary switchover and auto-recovery
• preventing chatter
• providing error burst detection and correction, holdover, and free
running capabilities
• complying with 2.0Mb CCITT specifications.
• communicating with software.
NTAK10 2.0 Mb DTI card
Option 11C and 11C Mini
Page 475 of 544
Technical Reference Guide