Siemens SIMATIC S7-400H Manual page 63

Use of redundant input and output modules
Note
If you have redundant I/O modules and have taken this into account in your
program accordingly, you might have to add a premium to the calculated
monitoring times, so that surging does not occur at the output modules.
A premium is required only if you operate modules redundantly from the following
table.
Table 5-2
ET200M: standard output modules
ET200M: HART output modules
ET200M: fail-safe output modules
ET200L-SC with analog output modules
ET200S with analog output modules or technology modules
Perform the following steps:
Determine the premium form the table. If several module types in the table are
used in Redundant mode, take the highest premium.
Add it to the monitoring times already determined.
Configuration of the monitoring times
When configuring the monitoring times you must note the following dependencies;
conformity will be checked by STEP 7:
max. scan-cycle time extension
> max. communication delay
> (max. blocking time for priority classes > 15)
> min. I/O hold time
If, in the case of link-up and update with master/standby switch-over, the CPUs
have been configured with different values for a monitoring function then the higher
of the two values will be used.
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Premium for the monitoring times of redundant I/O
Module type
Link-up and Update
Premium in ms
2
10
50
80
20
5-19