GE PACSystems RXi User Manual

Chapter 5. CPU Operation74 PACSystems* RXi Distributed IO Controller User Manual GFK-2816FMajor Phases in a Typical CPU SweepPhase ActivityHousekeeping The housekeeping portion of the sweep performs the tasks necessary to prepare for thestart of the sweep. This includes updating %S bits, determining timer update values anddetermining the mode of the sweep (Stop or Run.Input Scan During the input scan, the CPU reads input data from the embedded PNC.Note: The input scan is not performed if a program has an active Suspend I/Ofunction on the previous sweep.Application Program TaskExecution (Logic Window)The CPU solves the application program logic. It always starts with the first instruction inthe program. It ends when the last instruction is executed. Solving the logic creates anew set of output data.Interrupt driven logic can execute during any phase of the sweep. For details oncontrolling the execution of programs, refer to Chapter 6, Program Organization.A list of execution times for instructions can be found in Appendix A, CPU PerformanceData.Output Scan The CPU writes output data to the embedded PNC.If the CPU is in Run mode and it is configured to perform a background checksumcalculation, the background checksum is performed at the end of the output scan. Thedefault setting for number of words to checksum each sweep is 16. If the words tochecksum each sweep is set to zero, this processing is skipped. The backgroundchecksum helps ensure the integrity of the user logic while the CPU is in Run mode.The output scan is not performed if a program has an active Suspend I/O function onthe current sweep.Controller CommunicationsWindowCommunications on the Ethernet ports are serviced in this window. The CPU alwaysexecutes this window.Time and execution of the Controller Communications Window can be configured usingthe programming software. It can also be dynamically controlled from the user programusing Service Request function #3. The window time can be set to a value from 0 to 255milliseconds (default is 10 milliseconds).If the Controller Communications Window is set to 0, there are two ways to open thewindow: perform a power-cycle without the Energy Pack attached or go to Stop mode.BackplaneCommunications Window Even though the RXi Controller does not operate on a backplane, the BackplaneCommunications window still runs and parameters that affect it are implemented.The Backplane Communications Window defaults to Complete (Run to Completion)mode. This window can also run in Limited mode, in which the maximum time allocatedfor the window per scan is specified.The mode and time limit can be configured and stored to the CPU, or it can bedynamically controlled from the user program using Service Request function #4. TheBackplane Communications Window time can be set to a value from 0 to 255ms(default is 255ms). This allows communications functions to be skipped during certaintime-critical sweeps.Background Window CPU self-tests occur in this window.A CPU self-test is performed in this window. Included in this self-test is a verification ofthe checksum for the CPU operating system software.The Background Window time defaults to 0 milliseconds. A different value can beconfigured and stored to the CPU, or it can be changed online using the programmingsoftware.Time and execution of the Background Window can also be dynamically controlled fromthe user program using Service Request function #5. This allows background functionsto be skipped during certain time-critical sweeps.