GE PACSystems RXi User Manual

Chapter 4. Configuration38 PACSystems* RXi Distributed IO Controller User Manual GFK-2816F4.1.2 Controller Scan ParametersThese parameters determine the characteristics of CPU sweep execution.Scan ParametersSweep Mode The sweep mode determines the priority of tasks the CPU performs during the sweep anddefines how much time is allotted to each task. The parameters that can be modified varydepending on the selection for sweep mode.The Controller Communications Window, Backplane Communications Window, andBackground Window phases of the sweep can be run in various modes, based on the sweepmode.Choices:■ Normal mode: The sweep executes as quickly as possible. The overall Controller sweeptime depends on the logic program and the requests being processed in the windows andis equal to the time required to execute the logic in the program plus the respectivewindow timer values. The window terminates when it has no more tasks to complete. Thisis the default value.■ Constant Window mode: Each window operates in a Run-to-Completion mode. TheController alternates among three windows for a time equal to the value set for the windowtimer parameter. The overall sweep time is equal to the time required to execute the logicprogram plus the value of the window timer. This time may vary due to sweep-to-sweepdifferences in the execution of the program logic.■ Constant Sweep mode: The overall sweep time is fixed. Some or all of the windows at theend of the sweep might not be executed. The windows terminate when the overall sweeptime has reached the value specified for the Sweep Timer parameter.Logic ChecksumWordsThe number of user logic words to use as input to the checksum algorithm each sweep.Valid range: 0 through 32760, in increments of 8.Default: 16.ControllerCommunicationWindow Mode(Available only when Sweep Mode is set to Normal.) Execution settings for the ControllerCommunications Window.Choices:■ Complete: The window runs to completion. There is no time limit.■ Limited: Time sliced. The maximum execution time for the Controller CommunicationsWindow per scan is specified in the Controller Communications Window Timer parameter.Default: Limited.