Siemens SIMATIC PCS 7 CPU 410-5H System Manual page 286

Supplementary information
15.12 Link-up and update sequence
Minimum duration of input signals during update
Program execution is stopped for a certain time during the update (the sections below
describe this in greater detail). To ensure that the CPU can reliably detect changes to input
signals during the update, the following condition must be satisfied:
Minimum signal duration > 2 × time required for I/O update (DP and PNIO only)
+ call interval of the priority class
+ execution time for the program of the priority class
+ update time
+ execution time for programs of higher-priority classes
Example:
Minimum signal duration of an input signal that is evaluated in a priority class > 15 (e.g.,
OB 40).
Figure 15-24 Example of minimum signal duration of an input signal during the update
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CPU 410-5H Process Automation
System Manual, 09/2014, A5E31622160-AB