PROFIBUS DP is a serial fieldbus on shielded twisted pair, using RS-485, a fixed baud rate up to 12 Mbit/s, and a manually set node address from 0 to 125. PROFINET is industrial Ethernet: 100 Mbit/s full duplex, standard Ethernet cable and switches, devices identified by a device name rather than a DIP-switch address, and effectively no limit on node count. For new machines, PROFINET is the default choice — it carries IO data and IT traffic on one infrastructure and gives far richer diagnostics. PROFIBUS remains entirely valid for existing plants, and the two coexist through an IE/PB Link gateway rather than requiring a full rip-and-replace.
- Both are PROFIBUS & PROFINET International (PI) standards and share the same PROFIdrive and PROFIsafe profiles — device behaviour is largely portable between them.
- PROFIBUS uses a token-passing master/slave cycle; PROFINET RT uses prioritised Ethernet frames with a configured update time per device.
- PROFIBUS segments are bounded by baud rate and length; PROFINET links are 100 m per hop with switches extending the network indefinitely.
- The strongest practical argument for PROFINET is not raw speed — it is diagnostics, topology awareness and device replacement without a programming device.
The Short Version of the Difference
Both networks solve the same problem: getting process data between a controller and distributed field devices, deterministically, in an electrically hostile environment. They differ in the transport underneath.
PROFIBUS DP was designed in the early 1990s around RS-485 serial signalling. One master polls each slave in turn within a fixed bus cycle, and the cycle time is a predictable function of baud rate, node count and data size. It is proven, well understood, and still runs enormous quantities of installed plant.
PROFINET was designed around switched Ethernet. Instead of a shared serial line polled in sequence, each device has its own full-duplex link to a switch, and the controller exchanges data with each device at its own configured update time. The result is more bandwidth, easier expansion, and a network that carries engineering access, HMI traffic and IO data together.
The choice for a new project is rarely close any more. The interesting engineering questions are how to keep an existing PROFIBUS plant healthy, and how to bridge the two when a plant modernises in stages.
Side-by-Side Technical Comparison
| Characteristic | PROFIBUS DP | PROFINET |
|---|---|---|
| Underlying technology | RS-485 serial fieldbus | Switched Industrial Ethernet, 100 Mbit/s full duplex |
| Data rate | 9.6 kbit/s to 12 Mbit/s, one rate for the whole segment | 100 Mbit/s per link, independent of other devices |
| Media access | Master/slave polling with token passing between masters | Provider/consumer with prioritised real-time frames |
| Device addressing | Node address 0–125, set by DIP switch or software | Device name (DNS-conformant), IP assigned by the controller via DCP |
| Devices per segment | 32 per segment, 126 total with repeaters | Practically unlimited; bounded by bandwidth and controller capacity |
| Cable | Shielded twisted pair, purple sheath, defined cable types | Standard Cat 5e industrial Ethernet, green sheath, 2- or 4-pair |
| Distance | 1200 m at 9.6 kbit/s down to 100 m at 12 Mbit/s per segment | 100 m per copper link, extended indefinitely by switches; fibre for long runs |
| Connector | 9-pin D-sub with integrated terminating resistors | RJ45 or M12 D-coded |
| Termination | Mandatory at both segment ends, switched on the connector | None required |
| Topology | Line (bus), with repeaters for branches | Star, line, tree, ring — dictated by switch placement |
| Redundancy | Redundant master via specific configurations | MRP ring redundancy, system redundancy on S7-400H/S7-1500R/H |
| Diagnostics | Slave diagnostic telegram; segment faults need a bus analyser | Port-level statistics, topology comparison, timestamped diagnostic buffer |
| Device replacement | Set the address manually on the new device | Automatic name and IP assignment when topology is configured |
| Safety and drives | PROFIsafe, PROFIdrive over DP | Same PROFIsafe and PROFIdrive profiles over Ethernet |
Learn both networks on real Siemens hardware
Configure PROFIBUS DP and PROFINET IO in TIA Portal, then diagnose faults on live segments — Pune classroom or online.
Physical Layer, Cable and Connectors
PROFIBUS cable is a single shielded pair with defined impedance, and the network is a line — every device taps the same pair. The 9-pin D-sub connector carries a switchable terminating resistor network, and the two devices at the physical ends of a segment must have termination switched on and be powered, because the termination network draws its bias from the connector's 5 V supply. This detail explains one of the classic PROFIBUS faults: switching off a terminating device at the end of the line breaks communication for every device on the segment, not just that one.
PROFINET uses ordinary industrial Ethernet cable, typically 2-pair Cat 5e for 100 Mbit/s, terminated in RJ45 or, in wash-down and vibration environments, M12 D-coded connectors. Every link is a point-to-point run of up to 100 m into a switch port. There is no termination to configure and no shared segment to bring down. In exchange, cable quality and strain relief matter more, because a marginal Ethernet link degrades into intermittent CRC errors rather than failing cleanly.
One practical warning for both: unmanaged office-grade switches on a PROFINET IO network cause problems that look like device faults. Use switches that support the required prioritisation and, ideally, expose port statistics — the CRC error counter on a managed switch is often the fastest way to find a damaged cable.
Addressing and Device Identification
This is where the two feel most different in daily work.
On PROFIBUS you set a node address, historically with rotary switches or DIP switches on the device, sometimes in software. The address is the identity. Two devices with the same address produce a bus that will not communicate reliably, and finding the duplicate usually means walking the line with a laptop or a bus analyser.
On PROFINET you assign a device name — a text string following DNS rules — and the controller finds the device by that name at startup using DCP, then hands it the IP address from the project. Nothing needs to be set on the hardware itself. A brand-new device out of the box has no name, and the engineer or the controller writes one to it.
The consequence for maintenance is significant. On PROFIBUS a replacement device needs its address set correctly before it will work. On PROFINET, with topology configured, the controller recognises the new device by its position in the network — detected through LLDP neighbour information — and writes the name and address automatically. The spare comes out of the box and the line restarts.
PROFINET Conformance Classes and PROFIBUS DP Versions
Both standards have levels, and knowing which one a device supports prevents specifying hardware that cannot do what the application needs.
| Standard | Level | What it adds |
|---|---|---|
| PROFIBUS | DP-V0 | Cyclic process data exchange and basic diagnostics |
| PROFIBUS | DP-V1 | Acyclic parameter read/write, alarms — needed for smart field devices and drives |
| PROFIBUS | DP-V2 | Isochronous mode, slave-to-slave communication, clock synchronisation |
| PROFINET | Conformance Class A | Basic RT cyclic data over standard Ethernet infrastructure |
| PROFINET | Conformance Class B | Adds topology detection and network diagnostics — the practical minimum for maintainable plant |
| PROFINET | Conformance Class C | Adds IRT, isochronous real-time for synchronised motion control |
For a typical machine using remote I/O and drives for speed control, PROFINET RT at Conformance Class B is the sensible target. IRT and Class C belong to coordinated multi-axis motion, where axes must be synchronised to microseconds rather than merely fast.
Diagnostics: Where PROFINET Pulls Ahead
A PROFIBUS fault often presents as "the whole segment is down", because the network is a shared line. Isolating it means checking termination, walking the cable, and frequently reaching for a bus analyser to find reflections or a duplicate address. Experienced engineers get good at this, but it is a skill that takes time to build and equipment that is not always on site.
A PROFINET fault is usually attributable to a single link. The controller's diagnostic buffer timestamps the exact device that failed and returned, the topology view compares the configured layout with what LLDP actually reports, and a managed switch shows error counters per port. Free tools such as SIEMENS PRONETA scan the network and run a cable test without needing the project file.
That difference in diagnosability, more than raw bandwidth, is what usually justifies PROFINET in a maintenance-driven business case. A fault found in ten minutes instead of two hours pays for a lot of switch.
Choosing, Mixing and Migrating
| Situation | Sensible choice |
|---|---|
| New machine or new line | PROFINET — better diagnostics, easier expansion, single infrastructure for IO, HMI and engineering access |
| Adding a few devices to a healthy PROFIBUS line | Stay on PROFIBUS; a partial conversion adds a gateway and gains nothing |
| CPU upgrade with existing PROFIBUS field devices retained | New PROFINET CPU plus an IE/PB Link gateway to carry the existing DP segment |
| Coordinated multi-axis motion | PROFINET with IRT (Conformance Class C) |
| Long distances across a site | PROFINET over fibre between switches |
| Plant with Industry 4.0 / OPC UA reporting plans | PROFINET — the same Ethernet infrastructure carries OPC UA and SQL reporting traffic |
Staged migration is the normal path in a working plant. An IE/PB Link gateway presents an entire PROFIBUS DP segment to a PROFINET controller as if it were a PROFINET device, so the new CPU and the old field devices coexist. Machines then convert to PROFINET at their own overhaul schedule rather than in one shutdown.
Step-by-Step Lab: Compare Both Networks in TIA Portal
Hands-on- TIA Portal V17 or later. A CPU with both a PROFINET and a PROFIBUS interface (or an S7-1500 with a CM 1542-5 module) makes the comparison concrete, but the configuration steps can be completed offline without hardware.
- Optional but valuable: an ET 200SP on PROFINET and any DP slave on PROFIBUS.
- Estimated time: 25 minutes.
Build one project with both networks
Create a project with an S7-1500 CPU, add a PROFIBUS communication module, then add one IO device to the PROFINET interface and one DP slave to the PROFIBUS line.
Compare how each device is identified
Open the properties of the PROFINET device and note the device name and IP fields. Open the PROFIBUS slave and note the node address field. Try entering an address of 200 on the DP slave.
Look at the timing parameters side by side
On the PROFIBUS subnet properties, change the baud rate from 1.5 Mbit/s to 12 Mbit/s and note the calculated bus cycle time. On the PROFINET device, open the real-time settings and inspect the update time and accepted update cycles.
Open the topology view
Switch to the topology view and draw the port interconnections for the PROFINET device. Notice that the PROFIBUS slave does not appear there.
If you have hardware, break each network and compare the diagnostics
Download, go online, then interrupt each network in turn and open the CPU diagnostic buffer.
You have the distinction if you can state, without looking it up, that PROFIBUS timing is a property of the segment while PROFINET timing is a property of each device, and that a DP slave is identified by a number you set on the hardware while a PROFINET device is identified by a name the controller resolves at startup. Everything else — cable, connectors, diagnostics, replacement procedure — follows from those two facts.
Frequently asked questions
Is PROFINET simply a faster version of PROFIBUS?
No. They share the PI standards family and profiles such as PROFIsafe and PROFIdrive, but the transport is completely different: PROFIBUS is RS-485 serial with master/slave polling on a shared line, while PROFINET is switched Ethernet with a dedicated full-duplex link per device. Speed is one difference among many; addressing, topology, diagnostics and device replacement all work differently.
Can PROFIBUS and PROFINET devices exist in the same plant?
Yes, and this is the normal migration path. An IE/PB Link gateway presents an entire PROFIBUS DP segment to a PROFINET controller as though it were a PROFINET device, so a new CPU can keep existing DP field devices while new machines are built on PROFINET.
Do I still need terminating resistors on PROFINET?
No. Termination is a requirement of the RS-485 shared line used by PROFIBUS, where the two devices at the physical ends of a segment must have termination switched on and be powered. PROFINET uses point-to-point Ethernet links into switch ports and needs no termination at all.
How many devices can each network support?
PROFIBUS allows 32 devices per segment and 126 addresses in total, extended with repeaters. PROFINET has no comparable hard limit — the practical ceiling comes from available bandwidth, the controller's supported device count and the configured update times.
Is PROFIBUS obsolete?
No. It remains a supported standard with an enormous installed base, and a healthy PROFIBUS segment has no operational disadvantage for typical process I/O. New designs generally choose PROFINET, but converting a working PROFIBUS line simply because it is older rarely returns the investment.
Do I need IRT for drives on PROFINET?
Not for speed control. Standard PROFINET RT is sufficient for running drives from a PLC using PROFIdrive telegrams. IRT, which requires Conformance Class C hardware, is for coordinated multi-axis motion where axes must be synchronised to microsecond precision.