Chapter 4. CPU Operation
140 PACSystems* RX7i, RX3i and RSTi-EP CPU Reference Manual GFK-2222AD
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):
â– Run/Outputs Enabled
â– Run/Outputs Disabled
â– Stop/IO Scan
â– Stop/No IO
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