Siemens SIMATIC S7-400H System Manual page 171

Reaction to failure
Two-fiber optical ring and bus system
Because standard S7 connections are used here (the connection ends at the CPU of the
subsystem, in this case CPUa1), an error in the fault-tolerant system (e.g. CPUa1 or CPa1)
or an error in system b (e.g. CP b) results in total failure of communication between the
partner systems (see previous figures).
There are no bus system-specific differences in the reactions to failure.
Linking of standard and fault-tolerant systems
Driver block "S7H4_BSR": You can link an H system to an S7–400 using the "S7H4_BSR"
driver block. For more detailed information, contact the H/F Competence Center
Telephone: +49 (911) 895-4759
Fax: +49 (911) 895-4519
E-mail: hf-cc.aud@siemens.com
Alternative: SFB 15 "PUT" and SFB 14 "GET" in the fault-tolerant system: As an alternative,
use two SFB 15 "PUT" blocks over two standard connections. First call the first block. If
there was no error message when the block executed, the transfer is assumed to have been
successful. If there was an error message, the data transfer is repeated via the second block.
If a connection abort is detected later, the data is also transferred again to exclude possible
information losses. You can use the same method with an SFB 14 "GET".
If possible, use the mechanisms of S7 communication for communication.
S7-400H
System Manual, 09/2007, A5E00267695-03
11.6 Communication via S7 connections
Communication
171