Operating instructions

Industrial Ethernet SCALANCE X-100 and SCALANCE X-200 Product Line
Operating instructions, 09/2006, A5E00349864 Release 7
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IRT technology with SCALANCE X-200
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With STEP 7 as of V5.4, you can configure PROFINET devices that support data exchange
over isochronous real-time Ethernet (IRT). IRT frames are transferred deterministically over
planned communication paths in a fixed order to achieve the best possible synchronicity and
performance.
Supported devices
Topology-based IRT requires special network components that support planned data
transmission. X202-2 IRT, X204 IRT, X202-2P IRT, X201-3P IRT and X200-4P IRT support
topology-based IRT.
Constant bus cycle and isochronous real time now also available with PROFINET
The possibilities available for constant bus cycles and isochronous real time with PROFIBUS
DP are now available for PROFINET IO.
When using the constant bus cycle functionality in PROFIBUS DP, all nodes are
synchronized by a global control signal generated by the DP master.
In PROFINET IO with IRT, a sync master generates a signal with which the sync slaves
synchronize themselves. The sync master and sync slaves belong to a sync domain that is
assigned a name during project engineering. In principle, both an IO controller and an IO
device can adopt the role of sync master. A sync domain has exactly one sync master.
Relationship: Sync domain and IO systems
The important point is that sync domains do not need to be restricted to a PROFINET IO
system: The devices of several IO systems can be synchronized by a single sync master as
long as they are connected to the same Ethernet subnet.
On the other hand: A IO system may only belong to one sync domain.
Signal delays must be taken into account
If you use extremely precise synchronization intervals, the cable lengths (the associated
delays) must be taken into account. With the aid of a Topology Editor, you can enter the
properties of the cables between the ports of the switches. Based on this information and the
other configuration data, STEP 7 calculates the optimized sequence of the IRT
communication and the resulting update time.
Keeping network load within limits
To allow you to limit the network load resulting from extremely short update times, update
groups are configured for the IRT data. If only a few devices require the shortest update
times, these are assigned to the first update group. Each other update group has an update