GE PACSystems RXi User Manual

Chapter 5. CPU OperationGFK-2816F August 2015 77Constant Window ModeIn Constant Window mode, each sweep can consume a variable amount of time. The LogicWindow is executed in its entirety each sweep. The CPU alternates among the threewindows, allowing them execute for a time equal to the value set for the Constant Windowtimer. The overall CPU sweep time is equal to the time required to execute theHousekeeping, Input Scan, Logic Window, and Output Scan phases of the sweep plus thevalue of the Constant Window timer. This time may vary due to sweep-to-sweep variances inthe execution time of the Logic Window.Constant Sweep mode could be used for an application that requires a certain amount of timebetween the Output Scan and the Input Scan, permitting inputs to settle after receiving outputdata from the program.The value of the Constant Window timer can be any value from 3 to 255 milliseconds, andcan be set by the programming software or by the user program using Service Requestfunctions #3, #4, and #5.The following figure illustrates three successive sweeps in Constant Window mode. Note thatthe total sweep times may vary due to sweep-to-sweep variations in the Logic Window, butthe time given to the Communications and Background windows is constant. SomeCommunications or Background Windows may be skipped, suspended, or run multiple timesbased on the Constant Window time.CCHKINPUTOUTPUTCCBPCBGLOGICSWEEP n+1HKINPUTOUTPUTCCBPCBGSWEEP n SWEEP n+2HKINPUTOUTPUTCCBPCLOGIC LOGICCCSYSBGConstantWindowTimeAbbreviations:HK = HousekeepingCC = Controller Communications WindowBPC = Backplane Communications WindowBG = Background WindowTypical Sweeps in Constant Window Mode