Nortel Circuit Card, Installation Manual, Page: 759 / 908

NTAK79 2.0 Mb PRI card Page 759 of 906
Circuit Card Description and Installation
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 CS 1000S, CS 1000M Cabinet, and Meridian 1 PBX 11C Cabinet are
used as a master clock source for other systems in the network. Free-run mode
is undesirable if the CS 1000S, CS 1000M Cabinet, and Meridian 1 PBX 11C
Cabinet are 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 NTAK79 clock controller functions and features include:
• phase lock to a reference, generate the 10.24 MHz system clock, and
distribute it to the CPU through the backplane. Up to two references at a
time are accepted
• primary to secondary switchover (auto-recovery is provided)
• prevent chatter
• error burst detection and correction, holdover, and free running
capabilities
• compliance with 2.0Mb CCITT specifications
• software communication