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6
FUNCTIONS
6.9 Constant scan
(1) Definition of Constant Scan
The scan time differs because the processing time differs depending on whether the
instruction, which is used in the sequence program, is executed or not.
Constant scan is a function to execute the sequence program repeatedly while
maintaining the scan time at a constant time.
(2) Applications of constant scan
I/O refresh is performed before sequence program execution.
Using the constant scan function, the I/O refresh intervals can be made constant if the
sequence program execution time varies.
Scan time when constant scan is not used
Scan time when constant scan setting is set to 7 ms
END
0
END
0
5ms
Sequence program
END processing
END
0
END
0
Waiting time
5ms
2ms
7ms
Diagram 6.15 Constant scan operation
Sequence program
END processing
END 0
END 0
6ms
5ms
END
0
6ms
1ms
5ms
7ms
7ms
6.9 Constant scan
END
0
2ms
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