Chapter 5. Program Configuration and Operation Method
5-4
5.1.4 Scan Watchdog timer
WDT (Watchdog Timer) is the function to detect the program congestion by the error of hardware and software of PLC
CPU module.
(1) WDT is the timer used to detect the operation delay by user program error. The detection time of WDT is set
in Basic parameter of XG5000.
(2) If WDT detects the excess of detection setting time while watching the elapsed time of scan during
operation, it stops the operation of PLC immediately and keeps or clears the output according to
parameter setting
(3) If the excess of Scan Watchdog Time is expected in the program processing of specific part while performing
the user program (FOR ~ NEXT instruction, CALL instruction), clear the timer by using ‘WDT_RST’ Function
‘WDT_RST’ Function initializes the elapsed time of Scan Watchdog Timer and starts the time measurement from
0 again.
(For further information of WDT_RST Function, please refer to Instruction.)
(4) To clear the error state of watchdog, we can use the following method : power re-supply, PLC reset, mode
conversion to STOP mode.
Remark
1) The setting range of Watchdog Timer is 10 ~ 1000ms (Unit: 1ms).
WDT_RST instruction
execution
0 1 2 3 ….. …8 9
SCAN END
WDT Reset
0 1 2 …
count(ms)
0 1 2 … …6 7
SCAN END
0 1 2 …
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