The Difference between PROFIBUS and PROFINET

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We still get questions on the difference between PROFIBUS and PROFINET.  PROFIBUS is a classical serial fieldbus; PROFINET is an Industrial Ethernet.  The short answer is that PROFINET is faster with more bandwidth and larger messages.  Here is a more detailed look at the similarities and differences.

organization PI
application profiles same
concepts Engineering, GSDs
physical layer RS-485 Ethernet
speed 12Mbit/s 1Gbit/s or 100Mbit/s
telegram 244 bytes 1440 bytes (cyclic)^
address space 126 unlimited
technology master/slave provider/consumer
connectivity PA + others* many buses
wireless possible* IEEE 802.11, 15.1
motion 32 axes >150 axes
machine-to-machine No Yes
vertical integration No Yes
^with multiple telegrams: up to 232-65 (acyclic)
*not in spec, but solutions available

Because both were created and are supported by the same organization, there are similarities in the engineering concepts including the use of GSD files to define the hardware of each device,  GSD files for PROFIBUS are ASCII files while for PROFINET they are XML files.  The user benefits in moving from PROFIBUS to PROFINET because of the similarities.

The move from RS-485 to Ethernet is a move to a more modern technology.  Ethernet is ubiquitous.  Because PROFINET just uses standard Ethernet it is future-proof; as commercial Ethernet advances, PROFINET takes advantage.  For example, when PROFINET started, 100Mbit/s (Megabits per second) was common.  PROFINET can run just as easily on today’s Gigabit Ethernet (and higher).

The move to an Ethernet base provides for higher bandwidth, larger message size, and unlimited address space.  Although the specification does not limit the address space, individual controllers will have limits based on their processor and memory.

One reason PROFINET is faster is its use of the provider/consumer model.  Any node can communicate whenever it needs to.  Since Ethernet networks are now switched networks, there are no longer collisions on the network.  PROFIBUS achieved no-collisions by using a master/slave approach; the master was always in charge of the network and the nodes talked only when spoken to.

To connect to other networks, individual companies created gateways to do the translation.  PROFINET takes this one step further by defining proxies in the specification.  Proxies are like gateways in that they translate one network to another, but unlike gateways they are defined in an open standard.

PROFIBUS messages can be transmitted wirelessly, but they require proprietary radios from the same maker at both ends.  PROFINET, being standard Ethernet, easily uses WiFi and Bluetooth.

When should you use one versus the other?  Brownfield – use PROFIBUS. Greenfield – use PROFINET.  A brownfield location that already has PROFIBUS can continue to add PROFIBUS nodes.  Although if you need to add Ethernet functionality, it may pay to add a small projects-worth of PROFINET.  For a greenfield opportunity, definitely start with PROFINET – it’s the future.  For an introduction to that future, visit “PROFINET of Things.”

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