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LED displays depending on operating states and system states
CPU 1518HF-4 PN has the following LEDs for displaying the current operating state and
diagnostics status.
• RUN/STOP LED
• ERROR LED
• MAINT LED
The LEDs indicate the operating state of the respective CPU within the redundant system.
Operating states describe the behavior of a single CPU at a specific time. The combination of
the operating states of the CPUs forms the system state.
The following figure shows the possible operating states of the CPUs and the resulting system
states.
Figure 4-2
Operating states and system states
CPU 1518HF-4 PN (6ES7518-4JP00-0AB0)
Equipment Manual, 05/2021, A5E49868646-AA
Alarm, error and system messages
4.1 Status and error display of the CPU
29
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