Online And Diagnostic Tools; Status Leds - Siemens SIMATIC S7-1200 System Manual

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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.

Status LEDs on a CPU

The CPU provides the following status indicators:

– Solid yellow indicates STOP mode

– Solid green indicates RUN mode

– Flashing (alternating green and yellow) indicates that the CPU is in STARTUP mode

– Flashing red indicates an error, such as an internal error in the CPU, an error with the

– Defective state:

● 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.

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK

memory card, or a configuration error (mismatched modules)

- Solid red indicates defective hardware

- All LEDs flash if the defect is detected in the firmware