Mitsubishi Electric MELSEC-Q00U(J)CPU User Manual page 196

(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.
Internal processing time
END
WDT reset
(CPU module internal
processing)
● 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 execute the same scan time in every scan, use the constant scan function. (
194
Sequence program
Scan execution Scan execution
0
type program A type program B
Scan time
WDT measurement time
Internal
processing time
Scan execution
END 0
type program A
Next scan time
WDT reset
(CPU module internal
processing)
Page 119, Section 3.2)