Siemens SIMATIC S7-400H - Flowchart for OB1

Using I/O on the S7-400H
7-38
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
Read module A
first?
2nd attempt
== TRUE?
Access to
Read module A
Access to
module B
Yes No
I/O
access
error?
I/O
access
error?
Yes
Yes
Use value of
Read module A
Use
Use value of
module B
Use
No No
use
substitute
value
Read mod. A first
again in
future
2nd attempt: = TRUE
Yes Yes
No
No
2nd attempt
== TRUE?
Read mod. A first
any more in
future
2nd attempt: = TRUE
2nd attempt: = WRONG
Figure 7-14 Flowchart for OB1