Siemens SIMATIC ET 200AL, System Manual

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Functions
5.4 Media redundancy (ring topologies)
PROFINET with STEP 7
Function Manual, 05/2021, A5E03444486-AL
177
Rules for loading the devices of an MRP domain
When loading devices of an MRP domain, frame loops can occur and result in network failure
if there is an invalid MRP configuration.
Example: You change the MRP roles of several devices and consecutively load the
configuration into the devices involved. Configurations can arise that contradict the roles
mentioned above, for example, there may be devices that simultaneously have the "Manager"
and "Manager (auto)" roles in the ring.
To ensure that an invalid MRP configuration does not result in the failure of the network,
open the ring before loading.
Follow these steps:
1.
Open the ring.
2. Load the error-free and consistent MRP configuration from your project onto all the devices
involved and ensure that the devices are in data exchange mode (i.e. the application
relations (ARs) are set up).
3. Close the ring.
Boundary conditions
MRP and RT
RT operation is possible with the use of MRP.
Note
The RT communication is disrupted (station failure) if the reconfiguration time of the ring is
greater than the selected response monitoring time of the IO device. This is why you should
select a response monitoring time of the IO devices that is sufficiently large.
MRP and IRT
IRT mode is not possible together with MRP.
If you want to use media redundancy together with IRT in a ring, only use devices that
support MRPD.
MRP and TCP/IP (TSEND, HTTP, ...)
The TCP/IP communication with MRP is possible, because lost data packages are resent, if
applicable.
MRP and prioritized startup
If you configure MRP in a ring, you cannot use the "prioritized startup" function in PROFINET
applications on the devices involved.
If you want to use the "prioritized startup" function, then you must disable MRP in the
configuration (the device may also not be part of the ring).