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Chapter 5 Power Supply / CPU
5 -23
5.6 Functions
5.6.1 Self-diagnosis
1) Functions
(1) The self-diagnosis function permits the CPU module to detect its own errors.
(2) Self-diagnosis is carried out when an error occurs during PLC power supply is turned on or operating process.
If an error is detected, the system stops operation to prevent faulty PLC operation.
2) WDT (Watch dog timer) function
The watch dog timer is an internal timer of a PLC to detect the error of hardware and a sequence program. it is
changeable with parameter setting.
The CPU resets the watch dog timer before step 0 is executed (after the END processing is finished). When the END
instruction has not been executed within the set value due to an error occurred in the PLC or the delay of a sequence
program, the watch dog timer will times out. When a watch dog timer error is occurred, all outputs of the PLC are turned
OFF, and the ERR LED of the CPU will flickers. (RUN LED will be turned OFF) Therefore, when use FOR ~ NEXT or
CALL instruction, insert WDT instruction to reset the watch dog timer.
Refer the MASTER-K programming manual for details on the parameter setting.
3) I/O module check function
Mounting conditions of the loaded module are checked
4) Error history
When error occurs, Corresponding error code is stored in special relay F006.
0 WDT END 0 END
WDT Reset WDT Reset WDT Reset