Siemens SIMATIC S7-400H Manual page 197

Function
Direct communication
between DP slaves
Equidistance of DP slaves
Synchronizing DP slaves
Non-initialized local data
Runtime response
Delays and blocks
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Differences between Fault-Tolerant Systems and Standard Systems
Cannot be configured in STEP 7
No equidistance for DP slaves in the fault-tolerant system
The synchronization of DP slave groups is not possible.
SFC 11 "DPSYC_FR" is not supported.
When local data are stored in a data area (memory
markers, data blocks, etc.) or if they influence program
execution, the local data have to be initialized.
Non-initialized local data result in a synchronization error on
a fault-tolerant system. The system goes to Solo mode with
one CPU at STOP.
The command execution time is slightly slower on the CPU
417-4H than on the CPU 417-4 (refer to Operations list
S7-400 ). This is to be taken into account in all time-critical
applications. You may need to increase the scan cycle
monitoring time.
During update:
the asynchronous SFCs for data records are given a
negative acknowledgement
messages are delayed
all priority classes up to 15 are initially delayed
communications jobs are refused or delayed
finally all priority classes are blocked.
For more details refer to Chapter 5.
Constraint with CPU 417-4 H
D-3