Calculation Of The Max. Communication Delay; Calculation Of The Max. Scan-Cycle Time Extension; Influences On The Time Response - Siemens SIMATIC S7-400H Manual

Linking and Synchronizing
• The time T
structure. You can reduce it by using the following measures, for example:
– Store data that is frequently modified in different DBs to data that is modified
less often.
– Specify a smaller amount of working memory for the DBs.
If you reduce the time T
the risk of the update being aborted due to expiration of the monitoring times.

Calculation of the max. communication delay

We recommend using the following formula:
Maximum communication delay =
4 × (maximum blocking time for priority classes > 15)
The final time is determined by the process state and the communication load on
your system. This has to be taken to mean both the absolute load and also the
load in relation to the size of your user program. You may have to correct the time
if necessary.

Calculation of the max. scan-cycle time extension

We recommend using the following formula:
Maximum communication delay =
10 × (max. blocking time for priority classes > 15)
The final time is determined by the process state and the communication load on
your system. This has to be taken to mean both the absolute load and also the
load in relation to the size of your user program. You may have to correct the time
if necessary.
6.3.3

Influences on the Time Response

The period during which no I/O updates take place is primarily determined by the
following influencing factors:
• number and size of data blocks modified during the update
• number of instances of SFBs in the S7 communication information and SFBs
for generating block-related messages
• Modifications to the System During Operation
• settings via dynamic volume frameworks
• expansion of distributed I/O (with falling transmission rate and increasing
number of slaves the time required for I/O updates increases.)
6-24
indicates a guide value; this depends on your program
P15_AWP
without taking the measures stated, this increases
P15_AWP
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07