Siemens SIMATIC S7-400H Manual page 84

Using I/O on the S7-400H
Note
Variables BGA and PZF_BIT must also be valid outside OB1 and OB122. The
variable VERSUCH2, on the other hand, is used only in OB1.
Yes
Access to
module A
I/O
access
error?
2nd attempt
== TRUE?
No
Use value of
module A
Figure 6-4 Flowchart for OB1
6-12
2nd attempt: = WRONG
Read module
A first?
Do not read mod. A
first any more in future.
2nd attempt: = TRUE
Yes
No
Yes
Use sub-
stitute value
No
Read mod. A first
again in future.
2nd attempt:
TRUE
Yes
No
2nd attempt
== TRUE?
Yes
S7-400H Programmable Controller Fault-Tolerant Systems
Access to
module B
I/O
access
error?
No
Use value of
module B
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