6
-
4
6.2 Constant Scan
(1) Definition
Scan time of the CPU module is not constant because the processing time varies depending on the execution
status of instructions used in a sequence program.
Note1
This function allows sequence programs to be executed repeatedly, maintaining its scan time constant.
(2) 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.
Note1
Scan time without constant scan setting
Scan time with constant scan setting (7ms)
Scan time for multiple programs with constant scan setting (10ms)
Figure 6.1 Constant scan operation
Note6.1
Since the Basic model QCPU cannot execute multiple programs, it is not necessary to be conscious of the scan time
taken for execution of multiple programs.
Basic
END
5ms
0
END
0
END 0
END 0
6ms
5ms
Sequence program
END processing
END
5ms
0
END
0
2ms
6ms
END
0
1ms
5ms
END
0
2ms
7ms
7ms
7ms
Sequence program
END processing
Waiting time
8ms
2ms
10ms
9ms
1ms
10ms
Sequence program A
Sequence program B
Sequence program C
END processing
Waiting time
