AH500 Programming Manual 6.20.2 Explanation of Other Instructions Symbol: Explanation: 1. In the AH500500 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 STEP0 END WDT t1 t2 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.
6-430 API Instruction code Operand Function 1900 WDT P ─ Watchdog timer Pulse instruction 16-bit instruction (1 step) 32-bit instruction ─ AH500 ─