6
FUNCTIONS
6.17 Self-diagnostics Function
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6.17 Self-diagnostics Function
(1) Definition of Self-Diagnosis Function
The self-diagnosis is a function performed by the High Performance model QCPU
itself to diagnose whether there is an error in the CPU module.
The self-diagnosis function is used to prevent the CPU module erroneous operation
as well as preventive maintenance.
(2) Self-diagnostics timing
When an error occurs at power-on of the CPU module or during RUN/STOP of the
CPU module, an error is detected and displayed, and the operation of the CPU
module will be stopped by the self-diagnostic function.
Note that errors may not be detected by the self-diagnostic function depending on the
error occurrence status and the instruction to be executed. Even if the operation will
not be stopped by the self-diagnostics, establish a safety circuit outside the PLC so
that the entire system operates safely.
(3) Error checking
(a) LED ON
When the CPU module detects an error, it turns on ERR. LEDs.
(b) Error information storage destination and checking
When the CPU module detects an error, it turns ON the special relay (SM0, SM1)
and stores the information (error code) into the special register (SD0).
When multiple errors are detected, error codes of the latest errors are stored in
the special register SD0. For error detection, use special relays and special
registers in programs so that these devices can interlock with sequencers and
mechanical systems.
POINT
1. In the case of the Redundant CPU, the information of the error that occurred
in the other system is stored into the special relay (SM1610 to 1626) and
special register (SD1610 to 1636).
In any of the following cases, the other system error information is not stored.
• The other system is powered OFF/reset or has developed a hardware
failure.
• A watchdog timer error (error code: 5000, 5001) has occurred.
• Tracking cable fault (not installed, disconnected, failed, etc.)
2. The information of the errors that indicate the following CPU module statuses
are not stored into the special relays (SM0, SM1) or special registers (SD0 to
26). The ERR. LED is not turned on, either.
The error information is stored into the error history (
• System switching (from standby system to control system) switching has
occurred (Error message: CONTROL EXE. Error code: 6200)
• System switching (from control system to standby system) has occurred.
(Error message: STANDBY. Error code: 6210)
