Siemens SCALANCE X-200 Relationship: Sync domain and IO systems , Signal delays must be taken into account , Keeping network load within limits , IRT runs alongside real-time and TCP/IP communication

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.

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.

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.

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.