6 Application Instructions API 00-49 API 07 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 STEP0 END(FEND) WDT t1 t2 Using the set value in D1000 (default value: 200ms) to change the time for watchdog. Program Example: middle of the two parts, making scan time of the first half and second half of the program being less than 200ms. Assume the scan time of the program is 300ms, divide the program into two parts and place WDT instruction in the 300ms program END Dividing the program to two parts so that both parts' scan time are less than 200ms.
150ms program X0 WDT Watchdog timer reset 150ms program END DVP-PLC Application Manual 6-16 Mnemonic Function WDT P Watchdog Timer Refresh OP Descriptions Program Steps N/A WDT, WDTP: 1 steps PULSE 16-bit 32-bit EH3 EH3 ES EX SS SA SX SC EH SV EH3 SV2 ES EX SS SA SX SC EH SV ES EX SS SA SX SC EH SV SV2 SV2