Siemens SIMOTION D4 5-2 Series Commissioning And Hardware Installation Manual page 139

Isochronous operation and mode
Equidistant mode and isochronous mode function similar for PROFINET IO as for
PROFIBUS DP.
For PROFIBUS DP, in isochronous operation all nodes are synchronized using a Global
Control Signal created by the DP master.
In PROFINET IO with IRT, a sync master generates a signal to which sync slaves
synchronize themselves. Sync master and sync slaves belong to a sync domain which is
assigned a name via configuration. The role of the sync master can in principle be played by
an I/O controller as well as an I/O device. A sync domain has exactly one sync master.
Context: Sync domain and I/O systems
An important fact is that sync domains do not need to be limited to one PROFINET IO
system: The devices of several I/O systems can be synchronized by a single sync master,
provided they are connected to the same Ethernet subnet.
The following applies the other way around: An I/O system must only belong to a single sync
domain.
Signal propagation delays not negligible
For the extremely exact synchronization interval, line lengths, namely the associated delay
times, must be taken into consideration. You can use a topology editor to enter the
properties of the lines among the ports of the switches. STEP 7 uses this data and the other
configuration data to calculate the optimized process of the IRT communication and the
resulting updating time.
IRT runs in parallel to real-time and TCP/IP communication
Apart from IRT communication, for which a defined bandwidth is reserved within the update
time, RT communication and TCP/IP communication are also permitted within the update
time.
With RT communication (real-time communication), the cyclic data is transmitted between
I/O controller and I/O device, but without "best possible synchronism".
With non-synchronized I/O devices, data is exchanged automatically via RT communication.
Due to the fact that TCP/IP communication is also possible, other data, e.g. non-real-time
data, configuration data or diagnostic data, can be transported.
PROFINET IO controller
Typically, the function of a PROFINET IO controller is taken on by controllers (e.g.
SIMOTION C/P/D, SIMATIC S7 CPUs, ...).
The PROFINET IO controller takes on the master function for I/O data communication of the
distributed field devices. The function is comparable to a PROFIBUS DP master class 1.
SIMOTION D4x5-2
Commissioning and Hardware Installation Manual, 02/2012
Parameter assignment / addressing
5.6 Configuring PROFINET IO
139