Siemens SIMATIC S7-1200 Manual page 77

Use the CPU properties to configure how the CPU starts up after a power cycle.
The CPU performs a warm restart before going to RUN mode. Warm restart resets all non-
retentive memory to the default start values, but the CPU retains the current values stored in
the retentive memory.
Note
The CPU always performs a restart after a download
Whenever you download an element of your project (such as a program block, data block, or
hardware configuration), the CPU performs a restart on the next transition to RUN mode. In
addition to clearing the inputs, initializing the outputs and initializing the non-retentive
memory, the restart also initializes the retentive memory areas.
After the restart that follows a download, all subsequent STOP-to-RUN transitions perform a
warm restart (that does not initialize the retentive memory).
Easy Book
Manual, 11/2011, A5E02486774-04
Easy to create the device configuration
5.4 Configuring the operation of the CPU and modules
 In STOP mode
 In RUN mode
 In the previous
mode (prior to the
power cycle)
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