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097-55501-01 Issue 6 – June 2003 59
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Description
If both clocks are in the master shelf then each output card will receive
clocks from each, with preference given to the clock that is active (as seen on
the master shelf clock card). Only one output card is needed for full
functionality. Adding a second output card to the slot-pair provides
protection in the event that either of these output cards experiences a
failure.
To summarize, a given output on an expansion shelf can be expected to
function as long as there is at least:
• One clock card active in the master shelf AND
• One link cable connected (and operating properly) between the
master and expansion shelf AND
• One expansion controller card in the expansion shelf AND
• One output card in the slot-pair associated with the output of
interest.
1.10 Controlling Whether or Not an
Expansion Shelf is Expected in the
TimeHub System
It is important for the software in the TimeHub cards to have knowledge of
whether or not the user expects that there should be an expansion shelf (or
shelves) as part of the system. Without this information, it becomes
impossible for the software to know when an alarm/event should be
reported that has to do with an expansion shelf. As an example, suppose
that an expansion shelf has been configured into a TimeHub system but the
link cables have both been removed. In such a case, the user expects a
problem to be reported, to be informed that communication with the
expansion shelf has been lost. But what about a scenario where there is only
supposed to be a master shelf? In either of these situations, the software in
the master shelf detects that it cannot communicate with an expansion
shelf. In the first situation, the user wants to have a problem reported. In
the second situation, there is no problem.
N
OTE
: An expansion shelf will not work if its only path from
master to itself through an intermediate expansion shelf
requires that different links be used. For example, if only link 1
is used to connect from master to expansion shelf 1 and only
link 2 connects expansion shelf 1 to expansion shelf 2,
expansion shelf 2 will not receive a good link since its path from
the master is not continuous on a single link.
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