Siemens SIMATIC S7-400H Manual page 71

Table 5-3
The following assumptions were made for this formula:
80% of the data blocks are modified prior to delaying the interrupts of priority
classes > 15.
This value must be determined more accurately for fail-safe systems in
particular in order to avoid a time-out of the driver blocks (see Section 5.3.2).
Approximately 100 ms of update time are allowed for each megabyte of work
memory assigned by data blocks for currently running or held-back
communication functions.
Depending on the communication load of your programmable logic controller,
you have to add to or deduct from the setting of T
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Typical values for the user program share T
max. blocking time for priority classes > 15
Main memory data
500 Kbyte
1 Mbyte
2 Mbyte
5 Mbyte
10 Mbyte
Link-up and Update
of the
P15_AWP
T
P15_AWP
430 ms
800 ms
1.51 s
3.66 s
7.24 s
.
P15_AWP
5-27