Siemens SIMATIC S7-400H System Manual page 368

S7-400 cycle and response times
19.4 Communication load
Dependency of the actual cycle time on communication load
The figure below describes the non-linear dependency of the actual cycle time on
communication load. In our example we have chosen a cycle time of 10 ms.
Figure 19-6
Further effects on the actual cycle time
Seen statistically, the extension of cycle times due to communication load leads to more
asynchronous events occurring within an OB 1 cycle, for example interrupts. This further
extends the OB 1 cycle. How much it is extended depends on the number of events per
OB 1 cycle and the time required for processing these events.
Remarks
● Change the value of the "communication load" parameter to check the effects on the
● Always take the communication load into account when you set the maximum cycle time,
Recommendations
● Use the default setting whenever possible.
● Increase this value only if the CPU is used primarily for communication, and if time is not
368
Dependency of the cycle time on communication load
cycle time during system runtime.
otherwise you risk timeouts.
a critical factor for the user program! In all other situations you should only reduce this
value!
System Manual, 03/2012, A5E00267695-11
S7-400H