Time Monitoring - Siemens SIMATIC S7-400H System Manual

12.4

Time monitoring

Program execution is interrupted for a certain time during updating. This section is relevant
to you if this period is critical in your process. If this is the case, configure one of the
monitoring times described below.
During updating, the fault-tolerant system monitors the cycle time extension, communication
delay and inhibit time for priority classes > 15 in order to ensure that their configured
maximum values are not exceeded, and that the configured minimum I/O retention time is
maintained.
NOTICE
If you have not defined any default values for the monitoring times, make allowance for the
update in the scan cycle monitoring time. If in this case the update is cancelled, the fault-
tolerant system switches to standalone mode: The previous master CPU remains in RUN,
and the standby CPU goes into STOP.
You can either configure all the monitoring times or none at all.
You made allowances for the technological requirements in your configuration of monitoring
times.
The monitoring times are described in detail below.
● Maximum cycle time extension
● Maximum communication delay
S7-400H
System Manual, 03/2012, A5E00267695-11
– Cycle time extension: The time during the update in which neither OB 1 nor any other
OBs up to priority class 15 are executed. "Normal" cycle time monitoring is disabled
within this time span.
– Max. cycle time extension: The maximum permissible cycle time extension configured
by the user.
– Communication delay: The time span during the update during which no
communication functions are processed. Note: The master CPU, however, maintains
all existing communication links.
– Maximum communication delay: The maximum permissible communication delay
configured by the user.
Link-up and update
12.4 Time monitoring
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