Siemens SIMATIC S7-400H Manual page 68

Link-up and Update
8. From section 5.3.4 for 170 Kbytes user program data:
T
P15_AWP
Check: if T
9. Formula [3] now provides the recommended max. blocking time for priority
classes > 15:
T = MAX (194 ms, 140 ms)
P15
T = 194 ms
P15
If you enter 194 ms for the maximum blocking time for priority class > 15 in
STEP 7 it is ensured that in a change of signal during the update is always
recognized for signal durations of 1250 ms or 1200 ms.
Remedies for if it is not possible to calculate T
If no recommendation results from the calculation of the max. blocking time for
priority classes > 15 you can remedy this by various measures:
Reduce the watchdog interrupt cycle of the watchdog interrupt configured.
For particularly high T
systems.
Increase the transmission rate on DP master systems affected.
If the DP slaves have very different switch-over times and thus (generally) great
variations in T
If little load due to interrupts or parameter assignment is to be expected in the
individual DP master systems you can also reduce the T
approx. 20–30%. This will increase the risk of a station failure occurring in the
remote I/O.
The time T
structure. You can reduce it by, for example, placing data that is modified
frequently in different DBs to data that is modified less often. Reducing the time
T
P15_AWP
being aborted due to expiry of the monitoring times.
Calculation of the max. communication delay
We recommend the following formula:
Maximum comms delay = 4
classes > 15)
The final time is determined by the process state and the communication load on
your system. This has to be taken to mean both the absolute load and also the
load in relation to the size of your user program. You may have to correct the time
if necessary.
5-24
= 194 ms
= 194 ms < T
P15_AWP P15_HW
times divide the slaves into several DP master
TR
, divided these slaves into several DP master systems.
PTO
indicates a guide value; this depends on you program
P15_AWP
without taking the measures stated increases the risk of the update
(maximum blocking time for priority
S7-400H Programmable Controller Fault-Tolerant Systems
= 660 ms, continue with
P15
times determined by
TR
A5E00068197-04