Siemens SIMATIC CPU 410 System Manual page 122

Link-up and update
8.3 Time monitoring
Figure 8-1
Response to time-outs
If one of the times monitored exceeds the configured maximum value, the following
procedure is started:
1. Cancel update
2. Fault-tolerant system remains in standalone mode, with the previous master CPU in RUN
3. Cause of cancelation is entered in diagnostic buffer
4. Call OB 72 (with corresponding start information)
The standby CPU then reevaluates its system data blocks.
Following this, after at least one minute, the CPU tries again to perform the link-up and
update. If still unsuccessful after a total of 10 retries, the CPU abandons the attempt. You
yourself will then need to start the link-up and update again.
A monitoring timeout can be caused by:
● High interrupt load (e.g. from I/O modules)
● High communication load causing prolonged execution times for active functions
● In the final update phase, the system needs to copy unusually large amounts of data to
the standby CPU.
122
Meanings of the times relevant for updates
CPU 410 Process Automation/CPU 410 SMART
System Manual, 05/2017, A5E31622160-AC