Siemens SIMATIC S7-400H - Page 209

Using I/Os in S7–400H
13.5 Other options for connecting redundant I/Os
S7-400H
System Manual, 03/2012, A5E00267695-11
209
The sample program is based on the fact that following an access error on module A and its
replacement, module B is always processed first in OB 1. Module A is not processed first
again in OB 1 until an access error occurs on module B.
NOTICE
The MODA and IOAE_BIT variables must also be valid outside OB 1 and OB 122. The
ATTEMPT2 variable, however, is used only in OB 1.
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1R
1R
1R
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Figure 13-14 Flow chart for OB 1