86
8 RUNNING A PROGRAM
8.2 Scan Time
Accuracy of constant scan
The accuracy of the constant scan is 0.01ms. However, if processing, which should be executed during the waiting time from
the completion of the END processing to the start of the next scan, is being executed, the constant scan cannot finish even if
the constant scan time is reached. The constant scan may increase by the program execution time of the interrupt factor.
( Page 86 Precautions)
Precautions
• Processing of the program is stopped during the waiting time from the time the END processing is completed for the
program until the next scan starts. If any of the following processing requests is received during the waiting time, the
corresponding processing is executed.
• In redundant mode, when the CPU module is powered off, a hardware failure has occurred, or a tracking cable has a failure
in the standby system, the scan time will increase in the control system. When setting the constant scan, take one of the
following measures.
• In redundant mode, when the systems are switched in separate mode, the scan time of the control system will increase by
the increase of the standby system scan time.
• In redundant mode, in a program executed in both systems, the constant scan function is invalid for the standby system in
backup mode.
• Interrupt program
• Fixed scan execution type program
• Event execution type program which uses occurrence of an interrupt as a trigger
• Device/label access service processing
• Set the setting time of the constant scan by adding the increase in the scan time when an error occurs. ( Page 724 Increase in the scan time due
to tracking transfer)
• When a failure has occurred and a continuation error occurs due to the excess of constant scan time, clear the error. ( Page 208 Error Clear)
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