Supplementary information
16.11 Consistent data
CPU 410-5H Process Automation/CPU 410 SMART
254 System Manual, 10/2013, A5E32631667-AA
Figure 16-20 Example of redundancy with a fault-tolerant system, redundant bus system, and CP
redundancy on PC.
Double errors in the fault-tolerant system, e.g., CPUa1 and CPa2, and failure of the PC
result in a total failure of communication between the systems involved; see previous figures.
PC/PG as Engineering System (ES)
To be able to use a PC as Engineering System, you need to configure it under its name as a
PC station in HW Config. The ES is assigned to a CPU and is capable of executing STEP 7
functions on that CPU.
If this CPU fails, communication between the ES and the fault-tolerant system is no longer
possible.
Consistency of communication blocks and functions
On the S7-400H, communication jobs are not processed in the cycle control point but rather
in fixed time slices during the program cycle.
The byte, word and double word data formats can always be processed consistently in the
system, in other words, the transmission or processing of 1 byte, 1 word = 2 bytes or 1
double word = 4 bytes cannot be interrupted.
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