Siemens SIMATIC S7-400H Manual page 50

Link-up and Update
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:
Minimum signal duration > 2
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 5-3
5-6
time required for I/O update (for DP only)
+ 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
Processing time for the pro-
gram of the priority class –
for example, run time OB 40
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
S7-400H Programmable Controller Fault-Tolerant Systems
Processing time
of high-piority
priority classes
A5E00068197-04