PACSystems™ RX3i and RSTi-EP CPU Reference Manual Section 4
GFK-2222AK October 2019
CPU Operation 78
4.1 CPU Sweep
The application program in the CPU executes repeatedly until stopped by a command
from the programmer, from another device, from the RUN/STOP Switch on the CPU
module, or a fatal fault occurs. In addition to executing the application program, the CPU
obtains data from input devices, sends data to output devices, performs internal
housekeeping, performs communications tasks, and performs self-tests. This sequence of
operations is called the sweep.
The CPU sweep runs in one of three sweep modes:
In this mode, each sweep can consume a variable amount of time. The Logic
Window is executed in its entirety each sweep. The Communications and
Background Windows can be set to execute in Limited or Run-to-Completion
mode.
In this mode, each sweep begins at a user-specified Constant Sweep time
after the previous sweep began. The Logic Window is executed in its entirety
each sweep. If there is sufficient time at the end of the sweep, the CPU
alternates among the Communications and Background Windows, allowing
them to execute until it is time for the next sweep to begin.
In this mode, each sweep can consume a variable amount of time. The Logic
Window is executed in its entirety each sweep. The CPU alternates among
the Communications and Background Windows, allowing them to execute
for a time equal to the user-specified Constant Window timer.
Note: The information presented above summarizes the different sweep modes. For
additional information, refer to CPU Sweep Modes.
The CPU also operates in one of four RUN/STOP Modes (for details, refer to Run/Stop
Operations):
▪ Run/Outputs Enabled
▪ Run/Outputs Disabled
▪ Stop/IO Scan
▪ Stop/No IO
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