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Device Protocols

What is PROFIBUS and
PROFINET?

PROFIBUS and PROFINET are the dominant industrial communication protocols of the Siemens ecosystem — and by extension, of European and global discrete and process manufacturing. PROFIBUS is the legacy serial fieldbus for connecting distributed I/O, drives, and instruments to PLCs. PROFINET is its Ethernet successor. Both are managed by PI (PROFIBUS & PROFINET International) as open standards, but Siemens is the overwhelmingly dominant vendor in both ecosystems.

Last reviewed: 2026Reading time: ~10 minTopics: PROFIBUS DP, PROFINET RT, IRT, Siemens S7, S7 Ethernet, TOP Server, OPC UA

What are PROFIBUS and PROFINET?

PROFIBUS (Process Field Bus) was introduced in 1989 as a standardized serial fieldbus for connecting distributed I/O modules, variable speed drives, and intelligent field instruments to programmable logic controllers. PROFINET (Process Field Network) is its Ethernet successor, launched in 2003, which carries the same functional model over standard 100Mbps Ethernet. Together, they form the dominant I/O connectivity protocol family in the Siemens TIA (Totally Integrated Automation) portal ecosystem — which means they are ubiquitous in European manufacturing, automotive, and process industries, and present in substantial numbers everywhere Siemens hardware runs globally.

Both protocols are maintained as open standards by PI (PROFIBUS & PROFINET International), an organization with over 1,700 member companies. In principle, any vendor can build PROFIBUS or PROFINET devices. In practice, the ecosystem centers heavily on Siemens controllers (S7-300, S7-400, S7-1200, S7-1500) as masters communicating with Siemens ET 200 distributed I/O, Siemens SINAMICS drives, and third-party I/O and instrument vendors that support the standard.

The key distinction for OPC/SCADA engineers. PROFIBUS and PROFINET are I/O bus protocols — they connect PLCs to their distributed I/O racks, drives, and sensors in real time. They are not the protocol you use to read PLC data from SCADA or a historian. That role is filled by S7 Ethernet (also called S7 Protocol or ISO-on-TCP, running on port 102), which is the PLC-level communication protocol used by third-party OPC servers like TOP Server to read and write Siemens PLC tags. PROFIBUS and PROFINET run below the PLC; S7 Ethernet runs above it. Understanding this distinction avoids the common misconception that you need a PROFIBUS interface to read data from a Siemens PLC.

PROFIBUS vs. PROFINET: what changed

PROFIBUS DP
Process Field Bus — Decentralized Periphery
Legacy — still widely deployed

RS-485 serial fieldbus operating at up to 12 Mbit/s. A single PROFIBUS DP segment supports up to 126 devices (one master, 125 slaves) on a shielded twisted-pair trunk cable with drop lines to each device. The master polls each slave cyclically — the scan cycle time scales with the number of devices and the baud rate.

There are two variants: PROFIBUS DP (Decentralized Periphery) for fast cyclic I/O data exchange — the dominant variant, used for distributed I/O modules and drives; and PROFIBUS PA (Process Automation) for intrinsically safe process field instruments running on a slower 31.25 kbit/s bus with power delivered over the cable.

  • RS-485 physical layer, up to 12 Mbit/s
  • Up to 126 devices per segment, extendable with repeaters
  • Master-slave token passing architecture
  • Single-master (Class 1) or dual-master (Class 2 for parameterization)
  • GSD files define device profiles and I/O map
  • No native security, limited diagnostics vs modern Ethernet
PROFINET
Process Field Network — Ethernet-based I/O
Modern standard — all new Siemens designs

Standard 100Mbps Ethernet physical layer, using standard RJ45 connectors, standard managed switches, and standard Cat5e/Cat6 cable infrastructure. PROFINET retains the cyclic I/O data exchange model from PROFIBUS but dramatically improves performance, scalability, diagnostics, and integration with IT networks.

PROFINET defines three performance classes for different application requirements — RT for standard machine automation, IRT for motion control with microsecond precision, and the emerging TSN-FX for time-sensitive networking. All three use the same Ethernet physical layer; the difference is in how the protocol schedules data transmission.

  • Standard 100Mbps (or 1Gbps for IRT/TSN) Ethernet
  • No practical device limit per network segment
  • I/O Controller (PLC) to I/O Device (distributed I/O, drives) architecture
  • GSDML (XML-based) device description files replace GSD
  • Built-in topology detection, port-level diagnostics
  • Can share Ethernet infrastructure with IT networks (with proper VLAN segmentation)

PROFINET performance classes

PROFINET's three performance classes serve different application requirements while sharing the same Ethernet physical infrastructure:

RT — Real Time
1–10 ms
Standard cyclic I/O for machine automation. Uses standard managed switches. Sufficient for most discrete I/O, conveyor systems, and non-motion applications. The default class for most Siemens ET 200 deployments.
IRT — Isochronous Real Time
250 µs – 1 ms
Deterministic jitter below 1µs for motion control and synchronized multi-axis applications. Requires switches that support IRT (e.g., Siemens SCALANCE X with IRT support). Used with SINAMICS drives and SIMOTION/S120 motion controllers.
TSN-FX (Emerging)
<1 ms
PROFINET over IEEE 802.1 TSN (Time-Sensitive Networking). Combines deterministic real-time performance with standard IT Ethernet infrastructure, enabling OT and IT data on the same physical network without performance compromise. Supported in newer Siemens S7-1500 and ET 200SP hardware.

Siemens PLC families and their connectivity interfaces

Understanding which Siemens PLC family you are working with determines which protocols are available for OPC/SCADA connectivity. The critical point: all Siemens PLCs with Ethernet interfaces support the S7 communication protocol that TOP Server uses — PROFIBUS and PROFINET are the I/O bus running below the PLC, not the interface used by external applications to read PLC data.

PLC FamilyEraI/O busOPC/SCADA interfaceOPC UA embedded
S7-300 / S7-400
1990s–2010s (classic)
PROFIBUS DP
S7 Ethernet (ISO-on-TCP port 102) via CP or integrated Ethernet module
No
S7-1200
2009–present
PROFINET
S7 Ethernet (PUT/GET, port 102) via integrated Ethernet port
Yes, basic (TIA Portal V16+)
S7-1500 / ET 200SP (CPU)
2012–present (current)
PROFINET
S7 Ethernet via integrated Ethernet; OPC UA server built in
Yes — full UA server
WinCC / STEP 7 (legacy)
Legacy software
PROFIBUS DP / MPI
S7 via PC adapter, CP5611/5613 cards, or TCP gateway
No
SIMATIC ET 200SP (distributed I/O)
Current
PROFINET (as I/O device)
Via S7-1500 controller above it; can host CPU variant with own UA server
ET 200SP CPU variant only

How Software Toolbox connects to Siemens PLC data

The architecture for getting Siemens PLC data into OPC, SCADA, historians, and modern data platforms follows a consistent pattern regardless of whether the plant runs PROFIBUS or PROFINET on the I/O bus. The OPC server connects to the PLC itself — not to the I/O bus — using the S7 Ethernet protocol or, on modern S7-1500 hardware, directly via OPC UA.

1
Field devices on PROFIBUS/PROFINET
ET 200 distributed I/O, SINAMICS drives, valve manifolds, sensors — connected to the Siemens PLC over the I/O bus. The PLC reads these cyclically and stores values as PLC tags in its data blocks. PROFIBUS/PROFINET is completely internal to the Siemens automation layer.
↓
2
Siemens S7 PLC (S7-300/400/1200/1500)
The PLC processes I/O data and makes it available as named tags (DB blocks, inputs, outputs, markers) accessible via S7 Ethernet on port 102, or via its embedded OPC UA server (S7-1500 only). This is the interface external systems use — not PROFIBUS or PROFINET.
↓
3
TOP Server — Siemens S7 Ethernet driver
TOP Server connects to the PLC via S7 Ethernet (TCP port 102), reads tag data from data blocks, inputs, outputs, and markers, and exposes all values through OPC DA and OPC UA. For S7-1500 PLCs with embedded OPC UA, TOP Server can alternatively use its OPC UA client to connect directly, browsing the PLC's UA address space without a separate driver.
↓
4
SCADA / Historian / Analytics / UNS
Any OPC DA or OPC UA client — SCADA, historian, HMI, N3uron edge platform, or analytics tool — subscribes to Siemens PLC tags through TOP Server's OPC interface, or directly from the S7-1500's embedded UA server. The PROFIBUS/PROFINET bus is entirely transparent to these systems.

Why TOP Server cannot connect directly to PROFIBUS. PROFIBUS DP is a real-time serial fieldbus that runs at the I/O level of the Siemens automation hierarchy. It is designed for cyclic, millisecond-rate I/O data exchange between a PLC (master) and distributed I/O modules (slaves) — not for general-purpose data access from external applications. The correct and supported architecture is to connect above the PLC via S7 Ethernet, where all I/O data has already been processed and is available as named, scaled, contextualized PLC tags.

PROFIBUS/PROFINET vs. other industrial protocols

FeaturePROFIBUS DPPROFINET RTEtherNet/IPModbus TCP
Physical layerRS-485 serial100Mbps Ethernet100Mbps Ethernet100Mbps Ethernet
Governing bodyPI (PROFIBUS & PROFINET International)PIODVAModbus.org
Dominant vendorSiemens (S7-300/400)Siemens (S7-1200/1500)Rockwell Allen-BradleyUniversal
Typical cycle time1–10ms (depends on node count)1–10ms (RT), <1ms (IRT)1–10ms (implicit I/O)Poll-based, no cycle guarantee
Max devices126 per segmentNo practical limitNo practical limit247 per RS-485 bus

Software Toolbox products for Siemens connectivity

S7 Ethernet connectivity
TOP Server — Siemens S7 Ethernet driver
TOP Server's Siemens S7 Ethernet driver connects to the full Siemens S7 family — S7-200, S7-300, S7-400, S7-1200, S7-1500, WinCC, and LOGO! — using the S7 communication protocol over TCP port 102. It reads and writes data block items, inputs, outputs, markers (M), timers, and counters directly by address (e.g., DB5,REAL4, I0.0, Q2.3). The driver handles both optimized (S7-1200/1500) and classic (S7-300/400) data block structures, and supports connections through CP 343/443 communication processors as well as integrated CPU Ethernet ports.
OPC UA client (S7-1500)
TOP Server — OPC UA client driver
For modern Siemens S7-1500 PLCs with their embedded OPC UA server enabled in TIA Portal, TOP Server can connect as an OPC UA client rather than using the S7 Ethernet driver. This gives access to the PLC's full OPC UA address space, including the symbolic tag names configured in TIA Portal rather than raw memory addresses. The OPC UA connection uses standard port 4840 with certificate-based authentication. This approach is preferred for new S7-1500 deployments where TIA Portal OPC UA configuration is part of the project.
Edge + UNS for Siemens
N3uron
N3uron connects to Siemens S7 PLCs either via its built-in S7 driver or by subscribing to TOP Server's OPC UA output, contextualizes PLC tag data into ISA-95-structured topic paths, and publishes the result as a Sparkplug B MQTT stream. This bridges Siemens PLC data — which may have been running on a PROFIBUS or PROFINET I/O bus for decades — into a modern Unified Namespace architecture accessible to cloud analytics, AI platforms, and enterprise systems, without touching the underlying PLC configuration or I/O bus.

Frequently asked questions

Can I read PROFIBUS data directly with TOP Server?+−

Not directly, and this is the most important clarification for engineers approaching Siemens connectivity. TOP Server connects to the Siemens S7 PLC using the S7 Ethernet protocol — above the PLC. PROFIBUS runs below the PLC, connecting the PLC to its distributed I/O modules. The I/O data from those PROFIBUS devices is read by the PLC cyclically and stored in the PLC's process image and data blocks, where TOP Server can access it via S7 Ethernet.

The practical result is that you get all of the I/O data — because the PLC makes it available — without needing PROFIBUS hardware or software. The PROFIBUS bus is completely transparent from TOP Server's perspective.

What is the difference between PROFIBUS MPI and PROFIBUS DP?+−

MPI (Multi-Point Interface) is a Siemens-proprietary communication interface used for programming (connecting a PC running STEP 7 to the PLC for configuration and monitoring) and for peer-to-peer communication between S7-300/400 PLCs on the same rack or short distances. It runs at 187.5 kbit/s to 12 Mbit/s over the same RS-485 physical layer as PROFIBUS, but uses a different protocol stack.

PROFIBUS DP is the fieldbus for I/O devices — distributed I/O modules, drives, instruments. The two share physical cable and connector types but are used for different purposes. Modern S7-1200 and S7-1500 PLCs dropped the MPI interface entirely in favor of integrated Ethernet, which handles both programming (via TIA Portal) and peer-to-peer communication. If you encounter an MPI port on a legacy S7-300, it is for PC-to-PLC programming access via a PC adapter, not for data collection from SCADA.

My Siemens S7-1500 has an OPC UA server built in. Do I still need TOP Server?+−

It depends on your environment. If you have a single S7-1500 PLC and your SCADA or historian supports native OPC UA client connections, you can connect directly to the PLC's embedded UA server and may not need TOP Server for that specific device.

TOP Server remains valuable in multi-device environments — a plant with S7-300 (no UA), S7-1200 (basic UA), S7-1500 (full UA), Modbus instruments, and Allen-Bradley remote I/O. TOP Server consolidates all of these into a single OPC DA and UA endpoint, with consistent configuration, diagnostics, and a single support relationship. It also provides features the embedded PLC server does not: store-and-forward buffering, redundancy management, tag-level access control, and integration with the rest of the TOP Server driver library for non-Siemens devices on the same network.

What is SIMATIC NET and do I need it to connect TOP Server to a Siemens PLC?+−

SIMATIC NET is Siemens' own communication software layer, which includes PC software components for PROFIBUS and Industrial Ethernet access and the S7OPC server. It was historically required for third-party software to communicate with S7 PLCs over PROFIBUS (using a CP5611/5613 hardware card and the SIMATIC NET software stack).

TOP Server's Siemens S7 Ethernet driver communicates using ISO-on-TCP (RFC 1006 transport over port 102) and does NOT require SIMATIC NET software or any Siemens software to be installed on the TOP Server machine. It communicates directly with the PLC's Ethernet port using the S7 protocol over standard TCP/IP. This is a significant practical advantage — it removes the Siemens software dependency, avoids licensing costs for SIMATIC NET, and simplifies the deployment to a standard Windows TCP/IP network connection.

Is PROFIBUS being replaced by PROFINET in new installations?+−

Yes, definitively for new installations. Siemens has stated that S7-1200 and S7-1500 — their current PLC platforms — do not include integrated PROFIBUS DP ports. New Siemens automation designs use PROFINET for distributed I/O connectivity. The S7-300 and S7-400 platforms, which were the primary PROFIBUS hosts, reached end of sale milestones in 2023, though support and spare parts availability continues for existing installations.

PROFIBUS will remain present in brownfield plants for many years — possibly decades — because the installed base is enormous and replacing functioning PROFIBUS networks requires significant engineering effort and process downtime. But any engineer designing a new Siemens automation system today should plan around PROFINET from the start. For connectivity to SCADA and data systems, the approach is the same: connect above the PLC via S7 Ethernet or OPC UA, regardless of whether the I/O bus underneath is PROFIBUS or PROFINET.

What is the TIA Portal and how does it relate to PROFIBUS/PROFINET configuration?+−

TIA Portal (Totally Integrated Automation Portal) is Siemens' unified engineering software environment for programming, configuring, and commissioning all Siemens automation hardware — PLCs, HMIs, drives, and distributed I/O. It replaces the older STEP 7 (for S7-300/400) and WinCC Flexible tools with a single integrated environment.

PROFIBUS and PROFINET network topology, I/O device assignment, and cycle time configuration are all done within TIA Portal's device configuration view. This is entirely Siemens-internal — when you configure a PROFIBUS DP network in TIA Portal, you are defining the I/O bus that the PLC manages; you are not configuring anything that external systems like TOP Server interact with directly. External connectivity is configured separately: either via the S7 Ethernet driver in TOP Server (which only needs the PLC's IP address and the connection parameters), or by enabling and configuring the OPC UA server within TIA Portal for S7-1500 PLCs.

Connecting Siemens PLCs to your SCADA or data infrastructure?

Software Toolbox's Siemens S7 Ethernet driver connects to every S7 family — S7-300 through S7-1500 — without SIMATIC NET or any Siemens software dependency. For modern S7-1500 plants, the OPC UA client driver gives symbolic tag access directly from TIA Portal's address space.

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Ready to connect your Siemens PLCs?

Software Toolbox's engineers have been implementing Siemens S7 Ethernet connectivity since long before TIA Portal existed. Whether you are migrating from PROFIBUS, connecting S7-1500 via OPC UA, or consolidating a mixed-vendor plant, we can help.

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