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Chapter 5 Program Configuration and Operation Method<br />
2) Interrupt Operation (Time-driven, Internal Device)<br />
This is the method that stops the program operation in proceeding temporarily and carries out the<br />
operation processing which corresponds to interrupt program immediately in case that there occurs the<br />
status to process emergently during PLC program execution.<br />
The signal to inform this kind of urgent status to CPU module is called ‘interrupt signal’ and there is a timedriven<br />
method that operates program every appointed time. Besides, there is an internal device start<br />
program that starts according to the state change of device assigned inside.<br />
3) Constant Scan (Fixed Period)<br />
This is the operation method that performs the scan program every appointed time. This stands by for a<br />
while after performing all the scan program, and starts again the program scan when it reaches to the<br />
appointed time. The difference from constant program is the update of input/output and the thing to<br />
perform with synchronization.<br />
At constant operation, the scan time indicates the net program processing time where the standby time is<br />
deducted. In case that scan time is bigger than ‘constant’, ‘_CONSTANT_ER [F0005C]’ flag shall be ‘ON’.<br />
5.1.2 Operation Processing during Momentary Power Failure<br />
CPU module detects the momentary power failure when input power voltage supplied to power module is<br />
lower than the standard. If CPU module detects the momentary power failure , it carries out the operation<br />
processing as follows.<br />
1) Momentary power failure within 20ms<br />
Input power<br />
Within 20ms momentary power failure<br />
(1) Stops the operation in the output state when<br />
momentary power failure occurred.<br />
(2) If momentary power failure is released, the<br />
operation continues.<br />
(3) Output voltage of power module keeps the value<br />
within the standard.<br />
(4) Even if the operation stops by momentary<br />
power failure, timer measurement and interrupt<br />
timer measurement shall be executed normally.<br />
2) Momentary power failure exceeding 20ms<br />
• Restart processing like at power input shall be<br />
performed.<br />
Input power<br />
Momentary power failure exceeding 20ms momentary<br />
power failure exceed<br />
Notes<br />
1) Momentary power failure?<br />
This means the state that the voltage of supply power at power condition designated by PLC is<br />
lowered as it exceeds the allowable variable range and the short time (some ms ~ some <strong>do</strong>zens ms)<br />
interruption is called ‘momentary power failure ).<br />
5 - 2
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