Link-up and update
8.3 Time monitoring
CPU 410 Process Automation/CPU 410 SMART
130 System Manual, 05/2017, A5E31622160-AC
Performance values for link-up and update
User program share T
P15_AWP
of the maximum inhibit time for priority classes > 15
The user program share T
P15_AWP
of the maximum inhibit time for priority classes > 15 can be
calculated using the following formula:
T
P15_AWP
in ms = 0.7 x size of DBs in work memory in KB + 75
The table below shows the derived times for some typical values in work memory data.
Table 8- 3 Typical values for the user program part
1 MB 400 ms
5 MB 1.8 s
The following assumptions were made for this formula:
● 80% of the data blocks are modified prior to delaying the interrupts of priority classes >
15.
In particular for fail-safe systems, this calculated value must be more precise to avoid any
timeout of driver blocks (see section Determining the monitoring times (Page 123)).
● For active or queued communication functions, allowance is made for an update time of
approximately 100 ms per MB in the work memory occupied by data blocks.
Depending on the communication load of your automation system, you will need to add or
deduct a value when you set T
P15_AWP
.
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
● 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).
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