FIELDBUSES
PROFINET
Industrial Ethernet with cyclic I/O exchange between a controller and devices.
Who communicates with whom?
PROFINET IO uses a controller and configured devices identified on the network. After establishing an Application Relation, both sides provide cyclic data: the controller supplies outputs and the device supplies inputs/status. Devices do not wait for an individual master request every cycle as on Modbus RTU. Acyclic services cover parameters and diagnostics. An application feedback or diagnostic signal is required to prove that a physical action took place.
Voltage and waveform
PROFINET runs on Ethernet physical layers. For example, 100BASE-TX uses transformer-coupled differential twisted pairs. There is no universal PROFINET DC voltage on its data pair. A separate 24 V device supply or suitable PoE is not the voltage of an individual data bit.
Measuring with an oscilloscope
A DC meter tells little about Ethernet signal quality. Use suitable Ethernet test equipment or a properly rated differential probe, fixture and sufficient bandwidth to inspect the waveform or eye pattern against the PHY specification. Never connect a grounded scope clip to an arbitrary conductor.
The principle
A PROFINET IO controller exchanges cyclic process data with IO devices. Acyclic services support parameters and diagnostics. The configuration defines the expected modules and data.
An example
The animation illustrates cyclic updates. It does not reproduce actual Ethernet frames or real-time timing.
Important
An Ethernet link alone does not mean two devices can exchange PROFINET IO data; configuration and compatibility matter.