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3.2
Constant Scan
Scan time differs depending on the execution status of instructions used in sequence programs. This function
repeatedly executes sequence programs keeping their scan time constant.
(1) Application
I/O refresh is performed before every sequence program execution.
This function is used to maintain I/O refresh intervals constant even if the execution time of each sequence
program differs.
• Scan time without constant scan setting
• Scan time with constant scan setting (7ms)
END
• Scan time for multiple programs with constant scan setting (10ms)
(2) Constant scan time setting
Set a constant scan time value in the PLC RAS tab of the PLC parameter dialog box.
1.2.4)
When not executing the constant scan function, leave the constant scan time setting box blank.
Sequence program
END processing
END
0
END
0
5ms
Sequence program
END processing
0
END
0
Waiting time
5ms
2ms
7ms
Waiting time
8ms
10ms
Enter a value.
END 0
END 0
6ms
5ms
END
0
END
6ms
1ms
5ms
7ms
7ms
Sequence program A
Sequence program B
Sequence program C
END processing
2ms
9ms
1ms
10ms
CHAPTER 3 FUNCTIONS
0
2ms
(
Page 441, Appendix
119
3
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