Explanation Of Other Instructions - Delta AH500 Programming Manual

6.20.2 Explanation of Other Instructions

API Instruction code
1900 WDT
Symbol:
Explanation:
1. In the AH500 series PLC, there is a watchdog timer which is used to monitor the operation of
the system.
2. The instruction WDT is used to reset the watchdog timer in the PLC. If the program scanning
time exceeds 200 milliseconds, the error LED indicator is ON, and the PLC stops running.
3. The particular point when the watchdog timer acts:

The system is abnormal.

The execution of the program takes much time, and therefore the scam time is larger
than the setting value of the watchdog timer. There are two way users can use to improve
the situation.
1. Using the instruction WDT
2. Please refer to ISPSoft User Manual for more information about changing the
setting value of the watchdog timer.
Example:
Suppose the program scanning time is 300 milliseconds. After the program is divided into two parts,
and the instruction WDT is inserted between these two parts, the time it takes to scan either the first
part of the program or the second part of the program is less than 200 milliseconds.
Additional remark:
Please refer to ISPSoft User Manual for more information related to the setting of the watchdog
timer.
Operand
─
P
Pulse instruction 16-bit instruction (1 step) 32-bit instruction
STEP0
WDT
t1
Ch a pt er 6 Ap p l i ed I ns t r uc t i ons
─
AH500
END
t2
Function
Watchdog timer
─
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