Siemens SIMATIC ET 200AL, System Manual

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PROFINET with the redundant S7-1500R/H system
6.2 H-Sync Forwarding
PROFINET with STEP 7
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Function Manual, 05/2021, A5E03444486-AL
Conditions
• H-Sync Forwarding is not relevant for redundant S7-1500H systems. With the redundant
S7-1500H system, the H-Sync frames are transmitted exclusively via the fiber-optic cables.
• When you use PROFINET devices with more than two ports (e.g. switch) in the
PROFINET ring of an R-system, these devices must support H-Sync Forwarding.
H-Sync frames leave the PROFINET ring with a switch without H-Sync Forwarding. This
results in an additional load on the network. Another serious result is that the redundancy
of other R-systems in the network can fail or startup can be prevented.
• H-Sync Forwarding is recommended if you are using PROFINET devices with only 2
ports in the PROFINET ring of an R-system .
When you operate PROFINET devices without H-Sync Forwarding in the PROFINET ring of
the redundant S7-1500R/H system, the following scenario will result in an additional cycle
time increase:
1. The redundant S7-1500R system is in the RUN-Redundant system state.
2. The PROFINET cable which directly connects the two CPUs fails.
3. The PROFINET ring is interrupted.
4. The PROFINET ring is being reconfigured.
5. PROFINET devices without H-Sync Forwarding do not forward any H-Sync frames during the
reconfiguration time of the PROFINET ring.
6. The cycle time increases by the reconfiguration time of the PROFINET ring.
Figure 6-1
Failure of the PROFINET cable between the CPUs
If the cyclic program exceeds the cycle monitoring time, the timeout OB (OB 80) can be
started. Redundancy is lost if the time error OB (OB 80) is not present or the cycle time
was exceeded twice with OB 80.
Note
If failure of the PROFINET cable that directly connects the two CPUs of the redundant
S7-1500R system is unlikely, you can use PROFINET devices without H-Sync Forwarding in
the PROFINET ring of the redundant S7-1500R system.
Example: Both CPUs of the redundant S7-1500R/H system are located next to each other
in the control cabinet. In this case, it is unlikely that the PROFINET cable will fail.