Mitsubishi MELSEC-Q/L Programming Manual page 607

7.18
Other instructions
7.18.1 WDT, WDTP Watchdog timer reset
7.18.1
WDT, WDTP
WDT
WDTP
Internal Devices
Setting
Data
Bit Word
––
Function
(1) Resets watchdog timer during the execution of a sequence program.
(2) Used in cases where the scan time exceeds the value set for the watchdog timer due to prevailing conditions.
If the scan time exceeds the watchdog timer setting value on every scan, change the watchdog timer settings at the
peripheral device parameter settings.
(3) Make sure that the setting for t1 from step 0 to the WDT instruction and the setting for t2 from the WDT instruction to the
END (FEND) instruction do not exceed the setting value of the watchdog timer.
(4) The WDT instruction can be used two or more times during a single scan, but care should be taken in such cases,
because of the time required until the output goes OFF during the generation of an error.
(5) Scan time values stored at the special register will not be cleared even if the WDT or WDTP instruction is executed.
Accordingly, there are times when the value for the scan time for the special register is greater than the value of the
watchdog timer set at the parameters.
Operation Error
(1) There is no operation error in the WDT(P) instruction.
Program Example
(1) The following program has a watchdog timer setting of 200ms, when due to the execution conditions program execution
requires 300ms from step 0 to the END (FEND) instruction.
Command
Command
J \
R, ZR
Bit Word
Step 0
WDT
T1
Program where
scan time is
300 ms.
END
High
Basic
Process
performance
Zn
U \G
––
END (FEND)
T2
[When WDT instruction is used]
Program where
scan time is
150 ms.
WDT
Program where
scan time is
150 ms.
END
WDT, WDTP
LCPU
Redundant Universal
WDT
WDTP
Constants Other
605
1
2
3
4
4
6
7
8