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CHAPTER6 FUNCTIONS
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6.16 Watchdog T
ime
r (WDT
)
6.16 Watchdog Timer (WDT)
(1) Definition
This function serves as an CPU module internal timer to detect errors of CPU module hardware and sequence
programs.
(2) Setting and resetting
(a) Setting
The watchdog timer setting can be changed in the PLC RAS setting of PLC parameter.
The default is set to 200 ms.
The setting range is 10 to 2000 ms (in increments of 10ms).
(b) Reset
The CPU module resets the watchdog timer during END processing.
• The watchdog timer does not time up when the CPU module operates normally and the END/FEND
instruction is executed within the setting value of watchdog timer.
• The watchdog timer times up when the scan time of the sequence program is extended and the END/
FEND instruction could not be executed within the setting value of watchdog timer due to the hardware
failure of the CPU module or execution of an interrupt program/fixed scan execution type program.
(3) When the watchdog timer times up
"WDT ERROR" is detected and the following status occurs:
1) The CPU module turns off all outputs.
2) The RUN LED on the front of the CPU module turns off and the ERR. LED starts flashing.
3) SM1 turns on and the error codes 5000 and 5001 are stored in SD0.
(4) Precautions
(a) Watchdog timer error
An error is observed within the range of 0 to 10ms.
Set a watchdog timer while considering such an error.
