Cpu Operation - GE VersaMax PLC User Manual

7 CPU Operation

CPU Operation
For public disclosure
This chapter describes the operating modes of the VersaMax PLC CPUs, and shows the
relationship between the application program execution and other tasks performed by the
CPU.
CPU Operating Modes
The application program in a PLC executes repeatedly. In addition to executing the
application program, the PLC CPU regularly obtains data from input devices, sends data
to output devices, performs internal housekeeping, and performs communications tasks.
This sequence of operations is called the sweep.
• The basic operating mode of the PLC is called Standard Sweep mode. In this mode,
the CPU performs all parts of its sweep normally. Each sweep executes as quickly as
possible with a different amount of time consumed each sweep.
• The PLC may instead operate in Constant Sweep Time mode. In this mode, the CPU
performs the same series of actions but each sweep takes the same amount of time.
• The PLC may also be in either of two Stop modes:
− Stop with I/O Disabled mode
− Stop with I/O Enabled mode
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