Mitsubishi Electric MELSEC FX3U Programming Manual page 250

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
3. When FOR/NEXT instruction is repeated many times
Put WDT instruction between FOR and NEXT instructions.
248
FNC 08
K30000
FOR
Program
FNC 07
WDT
FNC 09
NEXT
8 Program Flow – FNC 00 to FNC 09
8.8 FNC 07 – WDT / Watchdog Timer Refresh