Siemens Industrial Ethernet Switches SCALANCE X-200 - Manual (Page 244)

IRT technology with SCALANCE X-200
SCALANCE X-200
244
Operating Instructions, 12/2011, A5E00349864-19
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
group with n times the update time compared with the previous group (n can be configured);
in other words, the group is updated less often and network load is reduced.
In STEP 7 V5.4, only one update group is planned.
IRT runs alongside real-time and TCP/IP communication
Apart from IRT communication for which a fixed bandwidth is reserved within the update
time, RT communication and TCP/IP communication are also permitted within the update
time.
In RT communication (real-time communication), the cyclic data is transferred between the
IO controller and IO device, however, without the "best possible synchronicity".
Unsynchronized IO device automatically exchange data using RT communication.
Since TCP/IP communication is also possible, other non real-time data or
configuration/diagnostic data can be transported.