Mitsubishi Electric MELSEC iQ-R-R04CPU - Constant Scan

1 RUNNING A PROGRAM
1.2 Scan Time
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1
Constant scan
Scan time is different for each scan because its processing time varies depending on whether instructions used in a program
are executed or not. By setting constant scan, the I/O refresh interval can be kept constant even when the program execution
time varies because the program can be executed repeatedly by keeping the scan time constant.
• When constant scan is set (Setting value = 7ms)
• When constant scan is not set
Setting constant scan
Constant scan can be set.
[CPU Parameter]  [RAS Setting]  [Constant Scan Setting]
Window
Displayed items
The setting time for the constant scan must be a value that satisfies the relational expression below.
"Watchdog timer setting time" > "Constant scan setting time" > "Maximum scan time of the program"
If the maximum scan time of the program is longer than the constant scan setting time, it is assumed as an
error to ignore the constant scan, and the scan time of the program is applied.
Item Description Setting range Default
Constant Scan Sets the constant scan time. • R00CPU, R01CPU, R02CPU: 0.5 to
2000ms (in increments of 0.1ms)
• Other CPU modules: 0.2 to 2000ms
(in increments of 0.1ms)

RnCPU
RnENCPU
RnSFCPU RnSFCPU RnPSFCPU RnPSFCPU RnPCPURnPCPU
(Standard) (Safety)(Standard) (Safety)
(Redundant) (Process)
END
5ms
0 END 0
2ms 6ms
END 0
1ms
5ms
END 0
2ms
7ms7ms 7ms
Program
END processing
Waiting time
END
5ms
0 END 0 END 0 END 0
6ms
5ms
Program
END processing