Resetting The Watchdog Timer - Mitsubishi Electric MELSEC iQ-F FX5 Programming Manual

Resetting the watchdog timer

WDT(P)
These instructions reset the watchdog timer in a program.
Ladder diagram
FBD/LD
EN ENO
Processing details
• These instructions reset the watchdog timer in a program.
• These instructions are used when the scan time exceeds the value set for the watchdog timer depending on the condition.
If the scan time exceeds the value set for the watchdog timer every scan, change the setting of the watchdog timer in the
parameter setting of the engineering tool.
• Design a program so that t1 from the step 0 to the WDT(P) instruction and t2 from the WDT(P) instruction to the END
(FEND) instruction do not exceed the setting value of the watchdog timer.
Step 0
t1
• The WDT(P) instruction can be used more than once in one scan. However, note that turning off the output takes some time
if an error occurs.
Precautions
• The time of the watchdog timer can be changed in the [RAS] tab of [CPU Parameter]. The default value is 200 ms.
• By overwriting the contents of SD8000 (watchdog timer time), the watchdog timer detection time can be changed using a
program. When the program shown below is input, the sequence program will be monitored with the new watchdog timer
time.
SM402
Initial pulse
(1): Watchdog timer time: 300 ms
(2): Refreshes the watchdog timer.
If the WDT instruction is not programmed, the value of SD8000 is valid during END processing.
Operation error
There is no operation error.
8 APPLICATION INSTRUCTION
394
8.3 Program Execution Control Instruction
END (FEND)
WDT
t2
MOV K300 SD8000
WDT
Structured text
ENO:=WDT(EN);
ENO:=WDTP(EN);
(1)
(2)