Siemens SIMATIC S7-1500 System Manual page 277

Once the backup CPU has caught up, both CPUs switch to the RUN-Redundant operating
state. The backup CPU establishes connections to the IO devices (only with system
redundancy S2 and R1) and the communication links are available again. Both CPUs process
the user program synchronously.
NOTE
High load during SYNCUP
The higher load during SYNCUP can prolong the program cycle.
If SYNCUP is taking too long and the displays are not showing any progress, you can abort
SYNCUP and optimize your user program. You can find more information under "SYNCUP
system state aborts".
NOTE
Setting a sufficiently long maximum cycle time
Configure a sufficiently long maximum cycle time for the CPUs. A temporary increase in the
cycle time can occur upon a system state transition SYNCUP → RUN-Redundant.
Effects of the SYNCUP system state
In SYNCUP, there are different effects on the execution of the user program and
communication functions. The effects are set out in the table below.
Table 11-11 Properties of SYNCUP
Procedure
Processing of the user program on the
primary CPU
Deleting, loading, generating and com­
pressing blocks
Processing communication functions
PG/PC operation
Test and commissioning functions, for
example "Monitor and modify tags", "Mon­
itoring (on/off)".
Connection handling in the primary CPU
Connection handling in the backup CPU
S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD
Effects during the SYNCUP system state
All priority classes (OBs) are processed. Processing is delayed during the snap­
shot. After the snapshot, the primary CPU immediately resumes user program
execution and asynchronous instructions are started.
Blocks cannot be deleted, loaded, generated or compressed.
The execution of parts of functions is limited and delayed. The system makes up
the delays in all functions after SYNCUP.
Depending on the SYNCUP phase, online connections from the PG/PC to the CPU
may not be possible. Existing connections are aborted.
Depending on the SYNCUP phase, no test and commissioning functions may be
possible.
All communication connections are initially aborted.
After the snapshot, the primary CPU re-establishes communication connections
with active connection establishment. Note that the CPU takes some time to re-
establish the communication connections.
The CPU re-establishes connection endpoints for communication connections
with passive connection setup.
All communication connections are initially aborted.
The backup CPU establishes connections (ARs) to the IO devices (only with sys­
tem redundancy S2 and R1).
The communication connections on the backup CPU become available during the
backup CPU catch-up process.
Commissioning
11.4 Operating and system states
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