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MELSEC-Q
7 FUNCTION
(c) The scan time value is not reset even if the watch dog timer is reset in the
sequence program.
The scan time value is measured to the END instruction.
0
Scan execution
type program A
Scan execution
type program B
Low speed execution type
program C
END 0
Scan time
Watchdog timer measured time
WDT reset (QCPU internal processing)
Sequence program Internal processing time
Next scan time
END
Low speed execution type
program C
Internal processing time
WDT reset
(QCPU internal processing)
Scan execution type
program A
Fig. 7.9 Watch dog Timer Reset
REMARK
• Scan time is the time from when the High Performance model QCPU starts
processing a sequence program at Step 0 until it restarts processing another
sequence program with the same filename at Step 0.
The scan time is not the same at every scan, and differs, depending on
• Whether the commands used are executed or not executed.
• Whether to execute or not an interrupt program and a fixed scan execution type
program.
• To execute at the same scan time at every scan, use the constant scan function.
For details of the constant scan function, see section 7.2.
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