3 CPU Unit Operation
3-4
CJ2 CPU Unit Software User’s Manual
The cycle time is the total time for overseeing, program execution, peripheral servicing, and I/O refresh-
ing. The cycle time normally fluctuates each cycle depending on the processing that is performed. Each
of these processes is performed within the cycle time. Refer to Section 12 CPU Unit Cycle Time for
information on how to calculate the cycle time.
Additional Information
A constant cycle time can be created by setting a minimum cycle time in the PLC Setup. The
minimum cycle time must be longer than any normal cycle time. For information on how to set a
minimum cycle time, refer to 10-2-1 Minimum Cycle Time.
The overhead time occurs for overseeing each cycle. The following items are checked.
• Battery error
•Memory Card
• DIP switch
• I/O bus
• User program memory
This is the processing time for instructions in the user program.
• The processing time includes instructions in cyclic tasks that are in READY status and instructions in
interrupt tasks for which the interrupt conditions are met. It does not include instructions that are
jumped in the programs.
• The processing time depends on the number of instructions and the specific instructions that are
used. It also depends on the operands that are specified (e.g., on the amount of data to be pro-
cessed).
• In RUN or MONITOR mode, internal processing time is required for instructions with OFF execution
conditions. In the following cases, internal processing is not performed and processing time is not
required.
• A cyclic task in WAIT status
• Instructions that are jumped for a JMP(004), CJP(510), or CJPN(511) instruction.
Additional Information
Consider the following programming if it is necessary to shorten the cycle time.
• Divide programs into cyclic tasks and place tasks into WAIT status when they do not need to
be executed.
• Use the JMP(004), CJP(510), and CJPN(511) instructions to jump instructions when they do
not need to be executed.
3-1-2 Cycle Time
Overseeing
Program Execution
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