S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
1309
Online and diagnostic tools
The CPU and the I/O modules use LEDs to provide information about either the operational
status of the module or the I/O.
The CPU provides the following status indicators:
● STOP/RUN
– Solid yellow indicates STOP mode
– Solid green indicates RUN mode
– Flashing (alternating green and yellow) indicates that the CPU is in STARTUP mode
● ERROR
– Flashing red indicates an error, such as an internal error in the CPU, an error with the
memory card, or a configuration error (mismatched modules)
– Defective state:
- Solid red indicates defective hardware
- All LEDs flash if the defect is detected in the firmware
● MAINT (Maintenance) flashes whenever you insert a memory card. The CPU then
changes to STOP mode. After the CPU has changed to STOP mode, perform one of the
following functions to initiate the evaluation of the memory card:
– Change the CPU to RUN mode
– Perform a memory reset (MRES)
– Power-cycle the CPU
You can also use the LED instruction (Page 450) to determine the status of the LEDs.
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