Chapter 4. CPU Operation150 PACSystems* RX7i, RX3i and RSTi-EP CPU Reference Manual GFK-2222AD4.5.1 CPU STOP ModesThe CPU has four modes of operation while it is in STOP Mode. The two most common are:STOP-I/O Enabled Mode▪ I/O Scan Enabled - the Input and Output scans are performed each sweep.STOP-I/O Disabled Mode▪ I/O Scan Disabled - the Input and Output scans are skipped.When the CPU is in STOP Mode, it does not execute the application program. You can configure whetherthe I/O is scanned during STOP Mode. Communications with the programmer and intelligent optionmodules continue in STOP Mode. Also, bus receiver module polling and rack reconfiguration continue inSTOP Mode.In both STOP Modes, the Controller Communications and Backplane Communications windows run inRun-to-Completion mode and the Background window runs in Limited mode with a 10 ms limit.The number of last scans can be configured in the hardware configuration. Last scans are completedafter the CPU has received an indication that a transition from Run to Stop or Stop Faulted mode shouldoccur. The default is 0.SVCREQ13 can be used in the application program to stop the CPU after a specified number of scans. AllI/O will go to their configured default states, and a diagnostic message will be placed in the CPU FaultTable.ControllerCommunicationsWindowBackplaneCommunicationsWindowBackground TaskWindowStart-of-SweepHousekeepingInput ScanOutput ScanExecutes inStop-I/O Scan Enabledmode onlyExecutes inStop-I/O Scan Enabledmode onlyRunstocompletionLimited(10ms)RunstoCompletionFigure 44: CPU Sweep in Stop-I/O Disabled and Stop-I/O Enabled Modes
