The User Program - Siemens SIMATIC S7-400H System Manual

3.7

The user program

The rules of developing and programming the user program for the standard S7-400 system
also apply to the S7-400H.
In terms of user program execution, the S7-400H behaves in exactly the same manner as a
standard system. The integral synchronization functions of the operating system are
executed automatically in the background. You do not need to consider these functions in
your user program.
In redundant operation, the user programs are stored identically on both CPUs and are
executed in event-synchronous mode.
However, we offer you several specific blocks for optimizing your user program, e.g. in order
to improve its response to the extension of cycle times due to updates.
Specific blocks for S7–400H
In addition to the blocks supported both in the S7-400 and S7-400H systems, the S7-400H
software provides further blocks which you can use to influence the redundancy functions.
You can react to redundancy errors of the S7-400H using the following organization blocks:
● OB 70, I/O redundancy errors
● OB 72, CPU redundancy errors
SFC 90 "H_CTRL" can be used to influence fault-tolerant systems as follows:
● You can disable interfacing in the master CPU.
● You can disable updating in the master CPU.
● You can remove, resume or immediately start a test component of the cyclic self-test.
● You can execute a programmed master to standby changeover. The following
Additional information
For detailed information on programming the blocks described above, refer to the STEP 7
Online Help.
S7-400H
System Manual, 03/2012, A5E00267695-11
changeovers are possible:
– The current standby CPU becomes a master CPU.
– The CPU in rack 0 becomes a master CPU.
– The CPU in rack 1 becomes a master CPU.
NOTICE
Required OBs
Always download these error OBs to the S7-400H CPU: OB 80, OB 82, OB 83,
OB 85, OB 86, OB 88, OB 121 and OB 122. If you do not download these OBs, the
fault-tolerant system goes into STOP when an error occurs.
S7-400H setup options
3.7 The user program
39