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6
FUNCTIONS
6.7 Self-diagnostics Function
(1) What the self-diagnostics function is
(2) Self-diagnostics timing
(3) Checking an error
(4) Checking the operation/error history
(5) CPU module operation when an error is detected (Stop error/
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6.7 Self-diagnostics Function
The self-diagnostics function diagnoses presence or absence of an error in the CPU
module by itself.
The objectives of the self-diagnostics function are the prevention of malfunction of the
CPU module and preventive maintenance.
If an error occurs when the CPU module is power on or while the CPU module is
running, the self-diagnostics function detects and displays the error, and executes the
CPU module operations stop etc.
(a) LEDlit
When the CPU module detects an error, it lights up the "ERR." LED.
(b) The storage destination and checking of the error definition
If the CPU module detects an error, it turns ON special relays (SM0 and SM1) and
stores the error definition (error code)in a special register (SD0).
If the CPU module detects multiple errors, it stores the error code of the latest
error into SD0.
Use the special relay and the special register in a program to establish the PLC or
mechanical system interlock.
The CPU module records 3000 incidents of the operation/error history.
(
Section 6.8)
The operation/error history can be checked by using GX Developer [Diagnostics]
[PLC diagnostics].
The operation/error history is backed up by battery even if the PLC is power-off.
continuation error)
When an error is detected by the self-diagnostics, the CPU module has the following
two types of operations.
(a) When an error that stops CPU module operations is detected
At the point when the CPUmodule detects the error, it stops operations and turns
all external output OFF. (Device memory output (Y) is held.)
The error which stops operation is referred to as a stop error.
(b) When an error that allows CPU module operations to continue is detected
Even when the CPUmodule detects the error, it continues to execute the program.
The error which continues operation is referred to as a continuation error.
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