Mitsubishi MELSEC QS Series, User Manual

Page: 123 / 264

6
FUNCTIONS
6.9 Constant scan
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(a) Setting time condition
As the constant scan time, set a value that satisfies the following relational
expression.
If the sequence program scan time is longer than the constant scan setting time,
the CPU module detects "PROGRAM SCAN TIME OVER" (error code: 5010).
In this case, the constant scan setting is ignored and the sequence program is
executed based on its scan time.
If the sequence program scan time is longer than the WDT setting time, the CPU
module detects a WDT error.
In this case, the program execution is stopped.
(4) Waiting time from when END processing is executed until next scan
starts
Sequence program processing is stopped during the waiting time from when the END
processing of a sequence program is executed until the next scan starts.
(5) Constant scan accuracy
Refer to CHAPTER 10 for the constant scan accuracy.
(WDT Set Time) > (Constant Scan Set Time)
> (Sequence Program maximum Scan Time)
Diagram 6.17 Operation when the Scan Time is longer than the Constant Scan setting time
0 1 2 3 4 1 2 3 4
0 0
1
END 0 END
2 3 4 1 2 3 4
0 END 0 END
3.5ms 0.5ms
4ms 4ms
3.5ms 3.4ms 0.6ms
4ms 5.3ms
5 ms
0.5ms
Scan where the constant scan is not normal
Constant scan setting
Constant
scan
Sequence
program