Response Electronics CL6011B Dokumentacja Pobierz pdf (Strona 72)

3Ć52 Theory of Operation: Communications

Original Ć June 1990CE4.2:CL6211

Note that certain tasks are periodic (caused by elapsed time intervals),

while other tasks are event driven (caused by the occurrence of some

external event, such as the receipt of an incoming request message).

Therefore, this can easily lead to the need to do more than one thing at

(nearly) the same instant in time. In this case, the highest priority item

will be completed first, then the next highest priority item will be

completed, etc.

Just as any human being can only be expected to do one task at a time,

so also the Regulatory Controllers can only perform one task (or

operation, if you will) at a time. Therefore, the priority (shown above) of

each task is used to determine which task is more important than

another task, when there is more than one task to be performed at a

given instant in time.

3.5.4 Trade-offs between Communications and Control

There is a limit to how many tasks the controller can perform within a

given period of time. The user can only configure a certain number of

functions for the controller to perform (see section A.1 in Appendix A

concerning controller loading). There is also some trade-off between

how much communications load the controller can support for a given

Control Task loading. A close examination of the controller loading

calculations will show that a fully configured Interactive or

Computing controller can spend more than 50 percent of its time

servicing the communications channel(s)!

For control applications where the controller configuration exceeds the

available CPU load, it may be necessary to examine the communications

support required in the given application, as well as the control loading

given by the configuration. Both should be considered when trying to

optimize a configuration application.

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Response Electronics CL6011B Dokumentacja Strona 72