Link-up and update
12.4 Time monitoring
S7-400H
System Manual, 03/2012, A5E00267695-11
167
12.4.4 Influences on time response
The period during which no I/O updates take place is primarily determined by the following
influencing factors:
● The number and size of data blocks modified during the update
● The number of instances of SFBs in S7 communication and of SFBs for generating block-
specific messages
● System modifications during operation
● Settings by means of dynamic quantity structures
● Expansion of distributed I/Os with PROFIBUS DP (a lower baud rate and higher number
of slaves increases the time it takes for I/O updates).
● Expansion of distributed I/Os with PROFINET IO (a higher update time and higher
number of devices increases the time it takes for I/O updates).
In the worst case, this period is extended by the following amounts:
● Maximum cyclic interrupt used
● Duration of all cyclic interrupt OBs
● Duration of high-priority interrupt OBs executed until the start of interrupt delays
Explicit delay of the update
Delay the update using SFC 90 "H_CTRL", and re-enable it only when the system state
shows less communication or interrupt load.
CAUTION
The update delay increases the time of standalone mode operation of the fault-tolerant
system.
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