Efficient Networks Siemens Sinamics S120 - Manual (Page 447)

Communication PROFIBUS DP/PROFINET IO
10.3 Communications via PROFINET IO
Drive Functions
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
447
10.3.3.4 PROFINET IO with IRTtop
The performance capability is significantly increased with PROFINET IRTtop for motion
control applications. A hardware support enables a significant increase in performance
compared with the present field bus solutions. By planning the message frame traffic in time
for IRTtop, a considerable data traffic optimization is achieved compared with IRTflex.
IRTtop is particularly suited for:
● The control and synchronization of axes via PROFINET
● A fast, isochronous I/O integration with short terminal-terminal times
For PROFINET IO with IRTtop, the synchronization of all devices on a shared Sync master
is necessary. The sum of all synchronized devices form a sync domain.
Send clock/refresh time
Within this time all cyclic and acyclic data (IRTtop data) is transferred. The send clock of 500
µs (as of FW2.5 SP1)/1 ms - 4 ms is the maximum range in which the send clock can be set.
The actual send clock that can be set depends on various factors:
● Bus load
● Type of devices used
● Computing power available in the controller
● Supported send clocks in the participating PROFINET devices of a sync domain
A typical send clock is, for example, 1 ms. However, it can be set in steps of 125 µs within
the limits of 500 µs (as of FW2.5 SP1)/1 ms to 4 ms.
Time-scheduled data transmission
Scheduling is the specification of the communication paths and the exact transmission times
for the data to be transferred. The bandwidth can be optimally utilized through
communication scheduling and therefore the best possible performance achieved. The
highest determinism quality is achieved through the scheduling of the transmission times
which is especially advantageous for an isochronous application connection.
The communication scheduling is performed by the engineering system. An IRT planning
algorithm is available for this. The schedule results must be transferred to each IO controller
through a download. The IO controller then loads the schedule results into the IO devices
during ramp-up. The communication with IRTtop is performed on the basis of these schedule
data.
The scheduled data transfer requires a hardware support for PROFINET IO with IRTtop in
the form of a communication ASIC (Application Specific Integrated Circuit). In order for the
scheduled communication not to be endangered by spontaneously transmitted IT message
frames, a certain part of the cyclic communication is reserved exclusively for the
transmission of IRTtop. This is called bandwidth reservation. The rest of the communication
cycle can be used for RT and IT communication.
Data exchange
Communication is generally also possible via network limits via routers. However,
PROFINET IO with IRTtop only runs within a sync domain.