STAR
TUP / TROUBLESHOOTING
5-14
Hardware
and Installation User Manual
5.2.4 Clearing
PLC Fatal Err
ors
A fatal error has occurred when both the following conditions hold:
PC GOOD LED is not lighted.
The DC GOOD LED on the power supply is on.
The
PLC enters a fatal error condition and ceases operation if a problem listed
below
occurs:
W
atchdog time-out: The microprocessor does not reset a watchdog
circuit periodically
.
Illegal operation code: The microprocessor receives an illegal
instruction.
Diagnostic test failure: The PLC fails a diagnostic test.
I/O fatal error: The PLC detects a non-recoverable I/O error
ROM diagnostic failure: The operating system EPROMs are found to
be invalid.
Operating system fatal error: The PLC detects a non-recoverable
error during execution.
Abnormal power loss: Power to the PLC is removed without proper
warning.
Dynamic Program Memory Diagnostics Error: The PLC determines a
checksum
error in the user EPROM/EEPROM or RAM.
When a fatal error occurs, the PLC takes the following actions:
The PC GOOD LED is turned off.
I/O ports are disabled. Discrete outputs are turned off, and word
outputs are held in their last valid state.
Communication ports are cleared and re-initialized.
Pending or queued tasks are cleared.
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