Siemens SIMATIC S7-1500 System Manual page 406

③STOP → STARTUP
Transition Description
System state STOP → STARTUP
transition
The redundant system switches to the STARTUP system state if:
• You set a CPU to RUN via the PG/PC or the display and the mode selector is
set to RUN
or
• You switch the mode selector from STOP to RUN.
The CPU that you switch from STOP to RUN first remains/becomes the primary
CPU. It switches to the STARTUP operating state and processes the startup
blocks.
The backup CPU remains in STOP.
STOP → STARTUP
Operating state
transition
After switch-on, the primary CPU switches to the STARTUP operating state if:
• The hardware configuration and program blocks are consistent
and
• You set the CPU to RUN via the PG/PC or the display and the mode selector
is set to RUN
or
• You switch the mode selector from STOP to RUN.
S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF
Commissioning
12.4 Operating and system states
Effects
The primary CPU clears
the non-retentive
memory and resets the
contents of non-
retentive data blocks to
the initial values of the
load memory. Reten-
tive memory and reten-
tive DB contents are
retained.
If there is a role change
between primary and
backup CPU, connected
IO devices are tempo-
rarily unavailable.
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