S7 Distributed Safety: Safety-Related Communication Via S7 Connections - Siemens SIMATIC S7 System Manual

Communication Options
3.6 Safety-Related CPU-CPU Communication
3.6.4

S7 Distributed Safety: Safety-Related Communication via S7 Connections

Introduction
In S7 Distributed Safety, safety-related CPU-CPU communication via S7 connections
between the safety programs of two F-CPUs takes place via configured S7 connections, as
in standard mode.
Safety-related CPU-CPU communication is not permitted via public networks.
Communication Overview
Figure 3-10
Communication via S7 Connections
Safety-related communication takes place with the aid of two fail-safe application blocks: the
F_SENDS7 block for sending data and the F_RCVS7 block for receiving data. These blocks
are called by the user in the respective safety program of the F-CPU. Using these fail-safe
application blocks, a user-defined amount of fail-safe data of data types BOOL, INT, WORD,
or TIME can be transferred in a fail-safe manner. The fail-safe data are applied to F-DBs
("F-communication DB") on the sending and receiving side.
Required User Steps
The user performs the following steps for safety-related communication via S7 connections:
1. Configure the S7 connection for each F-CPU in
2. Create an F-communication DB for both the send and receive data.
3. Initialize the variables of the F-communication DB for sending with variables.
4. Call F_SENDS7 in the safety program from where data are to be sent.
5. Call F_RCVS7 in the safety program in which data are to be received.
6. Assign parameters to F_SENDS7 and F_RCVS7.
7. Once the safety programs have been created, compile and download them to the
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S7 Distributed Safety: Communication between F-CPUs
appropriate F-CPU.
STEP 7 NetPro
.
Safety Engineering in SIMATIC S7
System Manual, 04/2006, A5E00109529-05