Troubleshooting Controller Fatal Errors; Cpu Fatal Error Indications; Causes Of Cpu Fatal Errors; Controller Responses To Fatal Errors - Siemens SIMATIC TI555 System Manual

7.3

Troubleshooting Controller Fatal Errors

CPU Fatal Error
Indications
Causes of CPU
Fatal Errors
Controller
Responses to Fatal
Errors
TI545/TI555 System Manual
A fatal error is indicated when both the following conditions are present.
CPU GOOD LED is not lighted.
The DC POWER GOOD LED on the power supply is on.
The CPU enters a fatal error condition and ceases operation if one of the
problems listed below occurs. AUX Function 20 or 29 displays the problem
that caused the CPU to enter the fatal error condition.
ROM diagnostic failure — the operating system EPROMs are found to
be invalid.
Watchdog time-out — the microprocessor does not reset a watchdog
circuit periodically.
Illegal operation code — the microprocessor receives an illegal
instruction.
Diagnostic test failure — the CPU fails a diagnostic test.
Operating system fatal error — the CPU detects a non-recoverable
error during execution.
Abnormal power loss — the CPU detects DC power failure without
advance warning from the power supply.
Dynamic Program Memory Diagnostics Error — the CPU determines a
checksum error in the user program memory (ladder or external
subroutine)
Fatal error due to EEPROM (EPROM) — the EEPROM (EPROM) is
bad.
When a fatal error occurs, the CPU attempts the following actions.
The CPU 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 communication tasks are aborted.
Troubleshooting
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