IEC 61158-1 Overview and guidance
Introductory part — scope, structure, overview of the fieldbus type families and their physical layer and data link layer specifications. The entry point to the multi-part series.
IEC 61158
IEC 61158 / IEC 61784 — Industrial Communication Networks (Fieldbus)
IEC 61158 defines the protocol specifications for industrial fieldbuses, while IEC 61784 specifies the communication profiles (CPFs) mapping real protocols — PROFIBUS, PROFINET, EtherNet/IP, Modbus, Foundation Fieldbus, DeviceNet and others — to the IEC framework. Together they are the normative basis for all major industrial fieldbus and industrial Ethernet standards.
Document structure
IEC 61158-2 Physical layer specification and service definition
Defines the physical medium — cable type, connector, signal levels, intrinsic safety (IS) variants for hazardous areas. Foundation Fieldbus H1 (31.25 kbit/s) and PROFIBUS PA physical layer defined here.
IEC 61784-1 Profile sets for continuous and discrete manufacturing — Communication profile families
The key normative reference: maps real-world protocol families (CPF 1 = Foundation Fieldbus, CPF 3 = PROFIBUS/PROFINET, CPF 2 = CIP/EtherNet/IP, CPF 15 = Modbus) to the IEC 61158 framework. The standard you cite when specifying a protocol.
IEC 61784-2 Additional profiles for industrial Ethernet
Extends CPF coverage to industrial Ethernet variants — PROFINET IRT, EtherNet/IP, EtherCAT, Powerlink, SERCOS III. Defines real-time performance classes.
IEC 61784-3 Functional safety fieldbuses (PROFIsafe, CIP Safety)
Defines the safety communication profiles on top of standard fieldbuses — PROFIsafe (CPF 3), CIP Safety (CPF 2), and others. Reference for SIL 2/3 safety instrumented systems using fieldbus.
IEC 61784-5 Installation of fieldbuses
Installation requirements — cable routing, grounding, shielding, maximum segment lengths. Practical design guidance for PROFIBUS DP, PROFIBUS PA, and Foundation Fieldbus H1 installations.
Key concepts
- Communication Profile Family (CPF)
(CPF) - IEC 61784-1 organises all industrial protocols into CPF numbers: CPF 1 = Foundation Fieldbus (FF H1, HSE), CPF 2 = CIP (EtherNet/IP, DeviceNet, ControlNet), CPF 3 = PROFIBUS DP/PA + PROFINET, CPF 15 = Modbus RTU/TCP. CPF numbers appear in datasheets and procurement documents.
- PROFIBUS DP
- Process Field Bus — Decentralised Periphery. RS-485 based, up to 12 Mbit/s, master-slave architecture. The dominant fieldbus in European discrete and process manufacturing. DP-V0 (cyclic I/O), DP-V1 (acyclic parameter read/write), DP-V2 (isochronous motion control). Phasing out in favour of PROFINET.
- PROFIBUS PA
- Process Application variant using IEC 61158-2 physical layer (Manchester-encoded, 31.25 kbit/s, intrinsically safe). Used to connect field instruments (transmitters, valves) in hazardous areas via a PA/DP segment coupler. Can power devices from the bus.
- PROFINET
- Process Field Net — Industrial Ethernet successor to PROFIBUS DP. TCP/IP based (100 Mbit/s or 1 Gbit/s). Three conformance classes: CC-A (standard TCP/IP), CC-B (real-time RT, ~1 ms cycle), CC-C (isochronous real-time IRT, ≤1 µs jitter). Dominant in new European automation projects.
- EtherNet/IP
- Industrial Ethernet protocol using standard IEEE 802.3 physical layer and TCP/IP + UDP, with the CIP (Common Industrial Protocol) application layer — the same application layer as DeviceNet and ControlNet. Dominant in North American automation (Rockwell ecosystem).
- Foundation Fieldbus (FF)
- H1 (31.25 kbit/s, IS-capable, 2-wire bus power) used for process instruments — the all-digital alternative to HART. HSE (High Speed Ethernet) for supervisory level. Supports function blocks running inside field devices (control in the field concept). Common in oil & gas and chemical sectors.
- Modbus RTU / Modbus TCP
- Simple master-slave protocol (1979, Modicon). RTU over RS-485/RS-232; TCP over Ethernet. Ubiquitous for simple device integration (drives, meters, analysers). No standard device description, no automatic device discovery — limited to simple register read/write.
Notes & guidance
Overview
IEC 61158 and IEC 61784 together form the normative framework for industrial fieldbus and industrial Ethernet protocols. Rather than defining a single universal protocol, IEC 61784-1 maps the major competing protocols into Communication Profile Families (CPFs), giving each a standard identity.
In practice, the choice of fieldbus is driven by industry sector, geography, and control system vendor:
| Protocol | Typical sector | Region | Trend |
|---|---|---|---|
| PROFIBUS DP | Discrete + process | Europe | Mature, being replaced by PROFINET |
| PROFIBUS PA | Process (IS areas) | Europe | Still deployed, FF H1 alternative |
| PROFINET | Discrete + process | Europe | Growing, new projects |
| EtherNet/IP | Discrete + process | Americas | Growing |
| Foundation Fieldbus H1 | Process (field devices) | Oil & gas, chemical | Stable |
| Modbus TCP/RTU | All sectors | Global | Legacy + simple integration |
| EtherCAT | Motion control | Global | High-performance servo |
Fieldbus Selection Principles
For new process plant projects (field instruments)
- HART (IEC 62591) remains dominant for simple 4–20 mA + digital instruments
- PROFIBUS PA or Foundation Fieldbus H1 for full digital bus, especially in hazardous areas with intrinsically safe power
- Wireless HART (IEC 62591) for difficult-to-wire locations
For new discrete/hybrid automation (I/O, drives, PLCs)
- PROFINET (Siemens ecosystem) or EtherNet/IP (Rockwell ecosystem) — choose based on the control system platform
- EtherCAT for high-speed motion control axes
Safety communication (IEC 61784-3)
Safety-rated I/O and drive integration requires a safety communication profile layered on the standard fieldbus: PROFIsafe on PROFINET/PROFIBUS, CIP Safety on EtherNet/IP.
PROFIBUS PA — Segment Design Rules
| Parameter | Value |
|---|---|
| Bit rate | 31.25 kbit/s |
| Max segment length | 1900 m (unrepeatered) |
| Max devices per segment | 32 (physical), typically 10–15 (bus power budget) |
| IS barrier variants | Zener barrier, galvanic isolator |
| Topology | Trunk + spurs |
Applicable industries
- process
- oil-and-gas
- manufacturing
- energy
- water-treatment
- pharmaceuticals