Minimum Signal Duration Of Input Signals During The Update - Siemens SIMATIC S7-400H Manual

Linking and Synchronizing

Minimum signal duration of input signals during the update

During the update, program scanning is stopped for a certain time (we will discuss
this subject in greater detail later). So that the change of an input signal can be
reliably detected by the CPU even during the update, the following condition must
be satisfied:
Min. signal duration > 2 ×× time required for I/O update (for DP only)
Example:
Minimum signal duration of an input signal that is evaluated in a priority class > 15
(for example, OB 40).
For DP only:
Time for updating the
I/O (worst case 2x)
Call interval
of the priority class
– for example, OB
40
Figure 6-3
6-6
+ call interval of the priority class
+ processing time for the program of the priority class
+ time for the update
+ processing time for programs of high-priority
priority classes
Time for updating
(75 ms + 0.7 ms per
KB for modified data
blocks)
Minimum signal duration
Example of minimum signal duration of an input signal during updating
Processing time for the pro-
gram of the priority class – for
example, run time OB 40
Processing time
of high-priority
priority classes
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07