Omron CJ2 CPU UNIT SOFTWARE User Manual page 65

Processing Cycle
The CPU Unit will repeatedly perform four processes (overseeing, program execution, I/O refreshing,
and peripheral servicing) after startup initialization. The time it takes to complete one cycle is called the
cycle time.
• Overseeing
This process prepares to execute the user program. It checks the hardware and software required for
processing. The time required for overseeing is called the overhead time.
• Program Execution
This process executes the instructions in the user program. The instructions in the user program are
executed when the operating mode is set to RUN or MONITOR mode. I/O processing for the instruc-
tions is performed on bits and words in the I/O memory areas in the CPU Unit.
• Peripheral Servicing
This process occurs when messages are required from Programming Devices or Units. Data is writ-
ten from the CX-Programmer or performed for instructions for Network Communications Units.
• I/O Refreshing
This process exchanges data with the Units by using the I/O memory areas. This process is always
performed after program execution. I/O refreshing is performed within the current cycle without inter-
ruption (i.e., without time slicing).
CJ2 CPU Unit Software User's Manual
3 CPU Unit Operation
3-3
3