Siemens S7-1200 System Manual page 82

PLC concepts
4.1 Execution of the user program
You can change the current operating mode using the "STOP" or "RUN" commands
(Page 792) from the online tools of the programming software. You can also include a STP
instruction (Page 263) in your program to change the CPU to STOP mode. This allows you
to stop the execution of your program based on the program logic.
82
NOTICE
Repairable faults can cause the CPU to enter STOP mode.
The CPU can enter STOP mode due to repairable faults, such as failure of a
replaceable signal module, or temporary faults, such as power line disturbance or erratic
power up event. Such conditions could result in property damage.
If you have configured the CPU to "Warm restart - mode prior to POWER OFF", the
CPU goes to the operating mode it was in prior to the loss of power or fault. If the CPU
was in STOP mode at the time of power loss or fault, the CPU goes to STOP mode on
power up and stays in STOP mode until it receives a command to go to RUN mode. If
the CPU was in RUN mode at the time of power loss or fault, the CPU goes to RUN
mode on the next power up providing it detects no errors that would inhibit a transition to
RUN mode.
Configure CPUs that are intended to operate independently of a STEP 7 connection to
"Warm restart - RUN" so that the CPU can return to RUN mode on the next power cycle.
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG