Watchdog Timer Refresh - Delta DVP-PLC Applications Manual

API Mnemonic
07 WDT
OP
N/A
Explanations:
1. No operand.
2. The watchdog timer in DVP series PLCs is used for monitoring the operation of the PLC system.
3. WDT instruction can be used to reset Watch Dog Timer. If the PLC scan time (from step 0 to END or when
FEND instruction is executed) exceeds 200ms, PLC ERROR LED will flash. The user will have to turn off PLC
and back On again. PLC will determine RUN/STOP status by RUN/STOP switch. If there is no RUN/STOP
switch, PLC will return to STOP status automatically.
4. When to use WDT:
a) When errors occur in the PLC system.
b) When the executing time of the program is too long, resulting in the scan time being larger than the content in
D1000, the user can improve the problem by the following two methods.
Using WDT instruction
Using the set value in D1000 (default value: 200ms) to change the time for watchdog.
Program Example:
Assume the scan time of the program is 300ms, divide the program into two parts and place WDT instruction in the
middle of the two parts, making scan time of the first half and second half of the program being less than 200ms.
300ms program
END
150ms program
X0
WDT
150ms program
END
6-14
P

Watchdog Timer Refresh

Descriptions
PULSE
ES EX SS SA SX SC EH SV ES EX SS SA SX SC EH SV ES EX SS SA SX SC EH SV
STEP0
Dividing the program to two parts
so that both parts' scan time are
less than 200ms.
Watchdog timer reset
6 Application Instructions API 00-49
Function
WDT, WDTP: 1 steps
16-bit
END(FEND)
WDT
t1 t2
Controllers
ES/EX/SS SA/SX/SC EH/SV
Program Steps
32-bit
DVP-PLC Application Manual