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MELSEC-Q
7 FUNCTION
(2) Setting the constant scan time
(a) The constant scan time is set at the "PLC RAS" tab screen in the “(PLC)
Parameter" dialog box.
The constant scan can be set in the range of 0.5 ms to 2000 ms.
A setting can be made in 0.5 ms units.
• When executing constant scan, set the constant scan time.
• When not executing a constant scan, leave the constant scan time blank.
[Example] When the constant scan is set to 10 ms.
(b) Set the set time of the constant scan longer than the maximum scan time of
the sequence program. Also, set the constant scan set time shorter than
the WDT set time.
(WDT Set Time) > (Constant Scan Set Time) > (Sequence Program maximum Scan Time)
If the sequence program scan time is longer than the constant scan set time,
the High Performance model QCPU detects PRG.TIME OVER (an error
code: 5010), the sequence program is executed with the scan time by
ignoring the constant scan.
0
1 2
3
4 1 2
3
4
00
1
END
0
END
2
3
4 1 2
3
4
0
END
0
END
3.5ms
0.5ms
4ms 4ms
3.5ms
0.5ms
3.4ms 0.6ms
4ms
Scan where the constant scan is not normal
Constant scan setting
Constant
scan
Sequence
program
5.3ms
5
ms
Fig. 7.2 Operation when the Scan Time is longer than the Constant Scan
If the time is longer than the WDT set time, the High Performance model
QCPU detects a WDT error and stops the program execution.
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