12.
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OVERVIEW OF PROCESSING PERFORMED BY THE QnACPU
12.3 Operation Processing for Instantaneous Power Failure
The QnACPU detects a momentary power failure when the input power voltage supplied
to the power supply module becomes lower than the specified range.
When the QnACPU detects an instantaneous power failure, the following operation
processing is performed.
(1) When an instantaneous power failure shorter than the allowable momentary power
failure period occurred:
(a) When an instantaneous power failure occurs, the output statuses are held and
the operation processing is suspended after the name of the currently accessing
file and error history have been stored.
(The timer count continues.)
(b) If there is an SFC continuous operation designation, system save processing is
executed.
(c) When power is restored, the operation processing will be continued.
(d) While the operation is interrupted due to an instantaneous power failure,
measurement of the watchdog timer (WDT) continues. For example, if 200ms is
set for the WDT parameter setting, power failure of 15ms in the scan time of
190ms will cause a watchdog timer error.
(2) When power failure longer than the allowable momentary power failure period
occurred:
The QnACPU starts from the first.
The operation processing is the same as that performed at PLC power-up or at CPU
module reset by the RUN/STOP key switch.
Fig. 12.1 Operation Processing for Instantaneous Power Failure
END
END
END
0
Occurrence of
instantaneous
power failure
Power supply
recovered
The PLC suspends the operation.
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