Siemens Simatic S7-1500R System Manual page 213

Commissioning
9.4 Operating and system states
⑤
Making up backup CPU lag
In phase
The communication connections on the backup CPU become available during the catch-up
process.
The backup CPU sends a status message on its program progress to the primary CPU at
each cycle control point.
The display of the primary CPU indicates the overtravel of the backup CPU.
Table 9- 9
Once the backup CPU has caught up, both CPUs switch to the RUN-Redundant operating
state. 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.
212
⑤
, the backup CPU catches up with the primary CPU.
Making up backup CPU lag
Primary CPU Backup CPU
S7-1500R/H redundant system
System Manual, 10/2018, A5E41814787-AA