Figure 28 real time communication – HEIDENHAIN PROFINET User Manual
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PROFINET IO data description
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PROFINET distinguishes between three real time classes for
transmission of time critical process data. The three RT classes
are:
Unsynchronized Real time communication
Industrial standard switches can be used.
Typical application area: Factory automation
Synchronized and unsynchronized data transmission
Special switches supporting IRT is needed
Typical application area: Factory automation
Isochronous Real Time, RT Class 3
The isochronous operation mode is used when real-time position-
ing with high performance is required. The basic principal is that all
PROFINET devices on the net are clock synchronized with the
controller using a global control broadcast enabling simultaneous
data accusation from all devices with microsecond accuracy. The
data exchange cycles for IRT are usually in the range of a few
hundred microseconds up to a few milliseconds. The difference to
real-time communication is essentially the high degree of deter-
minism, so that the start of a bus cycle is maintained with high
precision. The synchronization is monitored by sign-of life mes-
sages in Control word 2 (STW2_ENC) and Status word 2
Clock synchronized data transmission