Interrupts, diagnostics, error messages and system events 
  4.1 Status and error display of the CPU 
CPU 1513R-1 PN (6ES7513-1RL00-0AB0) 
Equipment Manual, 05/2021, A5E42009333-AC 
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LED displays depending on operating states and system states 
CPU 1513R-1 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