Communications Via S7 Connections; Communications Via S7 Connections - One-Sided Mode - Siemens SIMATIC S7-400H Manual

7.5

Communications via S7 Connections

Communications with standard systems
Fault-tolerant communications are not possible between fault-tolerant and standard
systems. The following examples illustrate the actual availability of the
communicating systems.
Configuration
Standard connections are configured with STEP 7.
Programming
If standard communications are used on a fault-tolerant system, all the
communication functions apart from "global data communications" can be used for
them.
The standard communication SFBs are used for programming communications
with STEP 7.
Note
The communication functions START and STOP act on exactly one CPU or on all
CPUs of the fault-tolerant system (for more details refer to the Reference Manual
System software for S7-300/400, System and standard functions ).
7.5.1 Communications via S7 Connections – One-Sided Mode
Availability
Availability is similarly enhanced by using a redundant system bus for
communications from a fault-tolerant system to a standard system.
If the system bus is configured as an optical two-fiber ring, communications
between the systems involved continue to exist in the event of the two-fiber optic
cable rupturing. The systems then communicate as if they were connected to a
bus system (line).
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Communications
7-13