Mitsubishi Electric MELSEC FX3U Programming Manual page 253

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
Caution
1. Limitation in the number of nesting
FOR-NEXT loop can be nested up to 5 levels.
Errors
1. Watchdog timer error
When FOR-NEXT loop is repeated many times, the operation cycle (D8010) is too long, and a watchdog
timer error may occur. In such a case, change the watchdog timer time or reset the watchdog timer.
2. Examples of wrong programs
The following programs are regarded as errors.
When NEXT instruction is located before FOR
instruction
When number of FOR instructions is not
equivalent to the number of NEXT instructions
FOR
FOR
FOR
1st
level
NEXT
NEXT
NEXT
→ For details on changing the watchdog timer time, refer to Subsection 37.2.2.
→ For resetting the watchdog timer, refer to WDT (FNC 07) instruction.
NEXT
FOR
FOR
FOR
NEXT
← Not programmed
NEXT
8 Program Flow – FNC 00 to FNC 09
8.10 FNC 09 – NEXT / End a FOR/NEXT Loop
FOR
FOR
NEXT
2nd 3rd
level level
FOR
NEXT
NEXT
When NEXT instruction does not exist
FOR
NEXT
When NEXT instruction is located after FEND or
END instruction
FOR
FEND
NEXT
END
NEXT
1st
level
2nd
level
1st
level
← Not programmed
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