Configuring Hardware and Communication Connections STEP 7.pdf

5 Configuring IRT Communication
5.1.1 Introduction: Isochronous Realtime Ethernet
In STEP 7 V5.4 you can configure PROFINET devices that support data exchange
over Isochronous Realtime Ethernet (IRT). IRT frames are transmitted in a
deterministic manner over planned communications paths in a specified sequence
in order to achieve the best possible synchronization and performance.
Topology-based IRT requires special network components that support planned
data transmission.
Constant Bus Cycle Time and Isochrone Mode now also with PROFINET
The constant bus cycle times and isochrone mode with PROFIBUS DP are now
available for PROFINET IO.
With PROFIBUS DP, all nodes operated with constant bus cycle times are
synchronized by a global control signal generated by the DP master.
With PROFINET IO with IRT, a "sync master" generates a signal with which the
"sync slaves" are synchronized. The sync master and the sync slaves belong to a
"sync domain", which is assigned a name during configuration. In principle, an IO
controller or an IO device can serve as a sync master. A sync domain has exactly
one sync master.
Correlation: Sync Domain and IO Systems
The important thing to recognize here is that sync domains do not have to be
restricted to one PROFINET IO system: The devices in several IO systems can be
synchronized by a single sync master, as along as they are all connected on the
same Ethernet subnet.
Conversely, the following also applies: An IO system may only belong to a single
sync domain.
Propagation Delay Cannot Be Neglected
With these extremely precise synchronization intervals, the lengths of the
connecting lines, that is, the related delay times, must be taken into account. By
using a topology editor, you can enter the properties of the lines between the ports
on the switches. Using this data along with the other data in the configuration,
STEP 7 will then calculate an optimized run-time for IRT communication and the
resulting update time.
Configuring Hardware and Communication Connections with STEP 7
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