Time Monitoring; Max. Scan-Cycle Time Extension; Max. Communication Delay - Siemens SIMATIC S7-400H Manual

Linking and Synchronizing
6.3

Time Monitoring

During the update program scanning is stopped for a particular duration.
Section 6.3 will be relevant to you if this duration is critical for your process. If so,
configure one or more of the monitoring times described below.
During the update the fault-tolerant system will monitor to check that the
scan-cycle time extension, the communication delay and the blocking time for
priority classes > 15 do not exceed the maximum values configured for them; at
the same time it ensures that the minimal I/O retention time configured is
maintained.
Notice
If you have not specified a value for any of the monitoring times then you must
take the update into account in the cycle monitoring time. If the update is
interrupted in this case, the fault-tolerant system will switch to single mode: The
CPU that has been the master CPU up to that point will remain in RUN mode and
the standby CPU will go to STOP mode.
You can either configure all the monitoring times or none.
You took the technological requirements into consideration in the monitoring times
configured.
The monitoring times are explained in more detail below.

• Max. scan-cycle time extension

– Scan-cycle time extension the time margin during the update in which there
is no execution of OB 1 (and no execution of any other OBs up to priority
class 15). During this margin of time the "normal" cycle time monitoring is
ineffective.
– Max. scan-cycle time extension the maximum permissible scan-cycle time
extension that you have configured.

• Max. communication delay

– Communication delay: the margin of time during the update during which no
communication functions are executed. (Note: The existing communication
links of the master CPU are maintained.)
– Maximum communication delay: the maximum permissible communication
delay that you have configured.
• Max. blocking time for priority classes > 15
– Blocking time for priority classes > 15: the margin of time during the update
during which no OB (and thus no user program) is executed and no more
I/O updates are performed.
– Max. blocking time for priority classes > 15: the max. permissible blocking
time that you have configured for priority classes > 15.
6-14
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07