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(b) Resetting a watchdog timer when a program is repeatedly executed between the FOR and
NEXT instructions
The watchdog timer can be reset by executing the WDT instruction in the sequence program.
To avoid the time up of watchdog timer while a program is repeatedly executed between the FOR and NEXT
instructions, reset the watchdog timer by the WDT instruction.
(c) Scan time when using the WDT instruction
The scan time value is not reset even if the watchdog timer is reset in the sequence program.
The scan time is measured up to the END instruction.
● A scan time is time required for the CPU module to operate the sequence program from step 0 and return
to the step 0 in the sequence program with the same file name.
● The scan time depends on the execution status of the following:
• Instructions used in the program
• Interrupt program and fixed scan execution type program
To keep the same scan time in every scan, use the constant scan function.
( Section 6.2)
Resetting watchdog timer when the a program is executed between the FOR and NEXT instructions
Figure 6.78 Resetting a watchdog timer when the program is executed between the FOR and NEXT instructions
Figure 6.79 Watchdog timer reset
FOR K1000
WDT
NEXT
Program repeatedly executed
WDT reset
Repeated in
1,000 times
MO
Internal processing time
Sequence program
Internal
processing time
Scan execution
type program A
Scan execution
type program B
WDT reset
(CPU module internal
processing)
END 0 END
Scan execution
type program A
0
Scan time
WDT measurement time
Next scan time
WDT reset
(CPU module internal
processing)