Siemens SIMATIC S7-400H System Manual page 161

Calculating the maximum inhibit time for priority classes > 15 (T
The maximum inhibit time for priority classes > 15 is determined by 4 main factors:
● As shown in Figure 12–2, all the contents of data blocks modified since last copied to the
● In the final update phase, all OBs are either delayed or inhibited. To avoid any
● In link-up and update operations with master/standby changeover (see section Link-up
● The technological conditions in your process also decide how long an I/O update can be
1. Based on the bus parameters in STEP 7, for each DP master system you must define:
2. For each IO subsystem from the STEP 7 configuration,
3. Based on the technical data of the switched DP slaves, define for each DP master
4. Based on the technical specifications of the switched DP devices, define
5. Based on the technological settings of your system, define:
S7-400H
System Manual, 03/2012, A5E00267695-11
standby CPU are once again transferred to the standby CPU on completion of the
update. The number and structure of the DBs you write to in the high-priority classes is a
decisive factor in the duration of this operation, and thus in the maximum inhibit time for
priority classes > 15. Relevant information is available in the remedies described below.
unnecessary extension of the maximum inhibit time for priority classes > 15 due to
unfavorable programming, you should always process the time-critical I/O components in
a selected cyclic interrupt. This is particularly relevant in fail-safe user programs. You can
define this cyclic interrupt in your configuration. It is then executed again right after the
start of the maximum inhibit time for priority classes > 15, provided you have assigned it a
priority class > 15.
sequence (Page 147)), you also need to changeover the active communication channel
on the switched DP slaves and switched IO devices on completion of the update. This
operation prolongs the time within which valid values can neither be read nor output. How
long this process takes is determined by your hardware configuration.
delayed. This is particularly important in time-monitored processes in fail-safe systems.
Note
For details, refer to the
Automation Systems, Fail-safe Signal Modules
internal execution times of fail-safe modules.
– T for the DP master system
TR
– DP changeover time (referred to below as T
– define the maximum update time of the IO subsystem (as of herewith named T
– PN changeover time (as of herewith named T
system:
– The maximum changeover time of the active communication channel
(referred to below as T
– the maximum changeover time of the active communication channel (as of herewith
named T ) for each DP master system.
Device_UM
– The maximum permissible time during which there is no update of your I/O modules
(referred to below as T
S7-400F and S7-400FH Automation Systems
).
SLAVE_UM
).
PTO
12.4 Time monitoring
)
P15
and
manuals. This applies in particular to the
)
DP_UM
)
PN_UM
Link-up and update
S7-300
)
max_Akt
161