User Program - Siemens SIMATIC S7-400H Manual

S7-400H Installation Options
2.5

User Program

The rules applicable to the design and programming of the standard S7-400
system apply similarly to the S7-400H.
The user programs are stored in an identical form in the two central processing
units and are executed simultaneously (event-synchronous).
From the viewpoint of user program execution, the S7-400H behaves in exactly the
same manner as a standard system. The synchronization functions are integrated
in the operating system and run automatically and totally in the background. There
is no need to take these functions into account in the user program.
In order to be able to react to the lengthening of the cycle time due to updating, for
example, a few specific blocks allow you to optimize your user program in this
respect.
Specific organization blocks and system functions for the S7-400H
Apart from the blocks that can be used on both the S7-400 and the S7-400H, there
are further additional blocks for the S7-400H with which you can influence the
redundancy functions.
You can react to redundancy errors of the S7-400H with the following organization
blocks:
OB 70, I/O redundancy errors
OB 72, CPU redundancy errors
Using system function SFC 90 "H_CTRL" you can inhibit and re-enable link-up and
updates of the 417-4H CPUs. You can also affect the scope and execution of the
cyclical self-test.
Note
With a fail-safe system, the periodic self-tests must not be inhibited and then
enabled again.
For more details refer to the manual S7-400F and S7-400FH Programmable
Controllers; Fail-Safe Systems.
Further information
You will find detailed information on the programming of the above-mentioned
blocks in the manual called Programming with STEP 7 and in the Reference
Manual called System Software for S7-300/400, System and Standard Functions .
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S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04