Efficient Networks S120 manual Profinet IO with IRTtop, Send clock/refresh time

Communication PROFIBUS DP/PROFINET IO 10.3 Communications via PROFINET IO

10.3.3.4PROFINET 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.

Drive Functions	447
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4