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Chapter 4 CPU Function
4 - 13
4.3.4 Error Handling
1) Classification of Errors
Errors occur due to various causes such as PLC option card system defect, system configuration
fault or abnormal operation result. Errors are classified into fatal error mode, which stops system
operation for system stability, and ordinary error mode, which continues system operation with inf
orming the user of its error warning.
The main factors that occurs the PLC option card error are given as followings.
• PLC option card hardware defect
• System configuration error
• Operation error during execution of the user programs
• External device malfunction
2) Operation mode at error occurrence
In case of error occurrence, the PLC option card write the error contents the correspond
ing flags and stops or continues its operation complying with its operation mode.
(1) PLC option card hardware defect
The system enters into the STOP state if a fatal error such as the CPU module def
ect has occurred, and continues its operation if an ordinary error such as operation
error has occurred.
(2) System configuration error
This error occurs when the PLC option card hardware configuration differs from the c
onfiguration defined in the PLC option card. The system enters into the STOP state.
(3) Operation error during execution of the user programs
It the numeric operation error of these errors occurs during execution of the user pr
ogram, its contents are marked on the error flags and the system continues its oper
ation. If operation time overruns the watchdog time or I/O modules loaded are not n
ormally controlled, the system enters into the STOP state.
(4) External device malfunction
The PLC option card user program detects malfunctions of external devices. If a fatal
error is detected the system enters into the STOP state, and if an ordinary error is
detected the system continues its operation.
Remark
1) In occurrence of a error, the state is to be stored in the representative system error
flag F006.
2) For details of flags, refer to Troubleshooting.