Industrial Fieldbus Protocols

Industrial networks typically implement fieldbus protocols for real-time and reliable distributed control to connect instruments and machines in a manufacturing plant, creating a system that can be easily and reliably controlled. Fieldbus standards are widely used, and there is a huge installed base of fieldbus-enabled equipment. However, most of these fieldbus standards are based on (legacy) serial communication protocol standards (similar to RS485 or RS232) that do not take advantage of the ubiquitous Ethernet technology.

With increasing levels of system complexity, most of these Fieldbuses are struggling to meet the requirements of platform interoperability and system performance. This is driving equipment manufacturers toward Ethernet-based communications that can deliver high performance, low cost, and high levels of interoperability. Many fieldbus standards have been integrated into Industrial Ethernet protocols for real-time communications and industrial connectivity, while preserving investments in fieldbus software and legacy equipment at the lowest level of control.

Table 1 lists a number of popular (serial) fieldbus protocols and their corresponding Ethernet-based industrial protocols.

Serial Protocols	Ethernet-Based Protocols
*Table 1. Popular Industrial Fieldbus and Industrial Ethernet Protocols*
CANopen	EtherCAT
CANopen	Ethernet Powerlink
DeviceNet/ControlNet	Ethernet/IP
LonWorks	Lon over Ethernet
Modbus-RTU	Modbus-TCP
PROFIBUS	PROFINET
SERCOS I/II	SERCOS III
-	VARAN
CC-Link	CC-Link IE
Fieldbus Foundation H1	Fieldbus Foundation HSE

CANopen

Controller Area Network (CAN) is a broadcast, differential serial bus standard used to operate in robust, electromechanically (noisy) environments. CANopen builds on CAN (e.g., data link and physical layers) in automation applications, where 100 percent data integrity is the requirement and where Ethernet may not be suitable.

DeviceNet/ControlNet (CIP)

DeviceNet is a device-level network offering robust, efficient data handling for industrial automation. ControlNet is a real-time, deterministic, and repeatable control-layer network for high-speed transport of data and messaging. The application layers for DeviceNet and ControlNet are based on the Common Industrial Protocol (CIP) layer, which is also used in Ethernet/IP. These protocols are now managed by the independent Open Device Vendors Association (ODVA).

LonWorks

LonWorks is a popular protocol standard used in building automation/control applications such as lighting and HVAC. LonWorks networks devices over a variety of media including twisted pair, power line, Ethernet, fiber optics, and RF.

Modbus-RTU

Modbus is an open, royalty-free serial communications protocol developed for programmable logic controller (PLC) applications. Modbus allows many devices to connect to the same network, such as interfacing a supervisory computer with a remote terminal unit (RTU) in supervisory control and data acquisition (SCADA) systems. The Modbus infrastructure is managed by Modbus-IDA, a group of independent users and suppliers of automation devices seeking to drive the adoption of this protocol standard.

PROFIBUS

The Process Field Bus (PROFIBUS) is a fieldbus protocol. Of the two PROFIBUS variants, decentralized peripherals and process automation (DP and PA), PROFIBUS DP is commonly used for sensor operation and actuators through a centralized controller in discrete manufacturing and process control. The lesser-used PA variant is used for monitoring measurement equipment. Through the years, PROFIBUS has gained wide acceptance in both production and process automation. PROFIBUS technology enhancements and promotions are directed by Profibus International (PI).

SERCOSI/II Interface

The Serial Real-time Communication System (SERCOS) interface provides a standard, real-time, high-performance communications interface between motion controls, digital servo drives, and input/output (I/O) devices. SERCOS is ideal for applications where the precise coordination of movement along multiple axes of motion control is critical. The official SERCOS Interface Standard document issued by the International Electrotechnical Commission (IEC) is IEC 61491. An industrial Ethernet version, SERCOS III, is also available. The group dedicated to developing, promoting, and expanding the adoption of the SERCOS digital interface for interconnecting motion controls, drives, I/Os, sensors, and actuators is made of the SERCOS Trade Association headed by the parent organization, SERCOS International.

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