Chapter 5 Program Configuration and Operation Method
5 - 2
(2) Interrupt operation (Cycle time, Internal device)
This is the method that stops the program operation in proceeding temporarily and carries out the
operation processing which corresponds to interrupt program immediately in case that there occurs the
status to process emergently during PLC program execution.
The signal to inform this kind of urgent status to CPU module is called „interrupt signal‟. There is a Cycle
time signal that operates program every appointed time and external interrupt signal that operates program
by external contact (“S” type: P000~P007, “E” type: P000~P003). Besides, there is an internal device start
program that starts according to the state change of device assigned inside.
(3) Constant Scan (Fixed Period)
This is the operation method that performs the scan program every appointed time. This stands by for a
while after performing all the scan program, and starts again the program scan when it reaches to the
appointed time. The difference from constant program is the update of input/output and the thing to
perform with synchronization.
At constant operation, the scan time indicates the net program processing time where the standby time is
deducted. In case that scan time is bigger than „constant‟, [F0005C] „_CONSTANT_ER‟ flag shall be „ON‟.
5.1.2 Operation processing during momentary power failure
CPU module detects the momentary power failure when input power voltage supplied to power module is
lower than the standard. If CPU module detects the momentary power failure , it carries out the operation
processing as follows.
If momentary power failure within 10 ms is occurred, main unit (CPU) keeps the operation. But, if
momentary power failure above 10 ㎳, the operation is stop and the output is Off. Restart processing
like at power input shall be performed.
(1) Momentary power failure within 10 ms
(2) Momentary power failure exceeding 10 ms
1) Momentary power failure?
This means the state that the voltage of supply power at power condition designated by PLC is
lowered as it exceeds the allowable variable range and the short time (some ms ~ some dozens ms)
interruption is called „momentary power failure‟ ).
CPU keeps the operation.
Restart processing like at power input shall
be performed.
Within 10 ms momentary
power failure
Momentary power failure exceeding 20ms
momentary power failure exceed
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