Interrupts/diagnostics alarms
6.1 Status and error displays
CPU 1512C-1 PN (6ES7512-1CK01-0AB0)
128 Manual, 12/2017, A5E40898741-AA
Meaning of the RUN/STOP, ERROR and MAINT LEDs
The CPU has three LEDs for displaying the current operating mode and diagnostics status.
The following table shows the meaning of the various combinations of colors for the
RUN/STOP, ERROR and MAINT LEDs.
Table 6- 1 Meaning of the LEDs
Missing or insufficient supply voltage on the CPU.
LED off
LED off
An error has occurred.
CPU is in RUN mode.
LED lit green
LED off
A diagnostics event is pending.
LED lit green
LED off
LED lit yellow
Maintenance demanded for the plant.
The affected hardware must be checked/replaced
within a short period of time.
LED lit green
LED off
LED flashes yellow
Maintenance required for the plant.
The affected hardware must be checked/replaced
within a foreseeable period of time.
Bad configuration
LED lit green
LED off
An error has occurred.
LED lit yellow
LED off
LED lit yellow
LED off
Firmware update successfully completed.
CPU is in STOP mode.
LED lit yellow
LED flashes red
LED flashes yellow
The program on the SIMATIC memory card is
LED flashes yellow
LED off
LED off
CPU is performing internal activities during STOP,
Download of the user program from the SIMATIC
memory card
CPU carries out a program with active breakpoint.
LED flashes
LED off
LED off
Startup (transition from RUN → STOP)