# 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.

- Source : https://industryhub.site/en/standards/iec-61158
- Body : IEC
- Family : Industrial Communication
- Status : current
- First published : 1999
- Latest revision : 2019 (Edition 7)
- Edition : 7
- Access : Paid (IEC webstore — price per part)
- Language : English

## Document structure

- **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 61158-2** — 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.

## 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

## References & further reading

- [IEC 61784-1 — IEC webstore](https://webstore.iec.ch/publication/6040)
- [PROFIBUS & PROFINET International (PI)](https://www.profibus.com)
- [ODVA — EtherNet/IP and CIP](https://www.odva.org)
- [FieldComm Group — Foundation Fieldbus and HART](https://www.fieldcommgroup.org)