Profibus
PROFIBUS, an abbreviation for Process Field Bus, is a standardized open fieldbus protocol designed for communication in industrial automation systems, enabling the interconnection of controllers, sensors, actuators, and other field devices over a single bus cable to facilitate real-time data exchange and control.[1] Developed as part of a collaborative project initiated by the German Federal Ministry for Research and Technology in 1987, the initial PROFIBUS specification was published in 1989, marking it as one of the earliest vendor-independent fieldbus standards.[2] Governed by PROFIBUS & PROFINET International (PI), a global association comprising approximately 1,800 member companies, PROFIBUS ensures interoperability across multi-vendor environments and complies with international standards such as IEC 61158.[3] The protocol operates on the physical and data link layers of the OSI model, supporting transmission speeds up to 12 Mbps for its primary variant and using RS-485 signaling for robust, noise-resistant communication in harsh industrial settings.[1] PROFIBUS features a master-slave architecture with token-passing for multi-master setups, allowing cyclic and acyclic data transfer for process monitoring, diagnostics, and parameterization.[4] Its design emphasizes simplicity, cost-effectiveness, and scalability, making it suitable for applications ranging from discrete manufacturing to continuous processes.[1] PROFIBUS encompasses three main variants tailored to specific needs: PROFIBUS-FMS (Fieldbus Message Specification), an early version for peer-to-peer messaging in high-level factory networks; PROFIBUS-DP (Decentralized Peripherals), optimized for high-speed, deterministic communication with distributed I/O in factory automation; and PROFIBUS-PA (Process Automation), which uses a specialized MBP (Manchester Bus Powered) physical layer for intrinsically safe operation in hazardous process environments like chemical and oil & gas industries.[4] Extensions such as PROFIsafe integrate functional safety, while PROFIdrive supports standardized drive control, enhancing its versatility.[5] These variants allow seamless integration from field level to higher-level systems, promoting efficient automation architectures.[1] Since its inception, PROFIBUS has achieved widespread adoption, with over 70 million devices installed globally as of the end of 2024, establishing it as the leading fieldbus technology in terms of market penetration and reliability.[6] Its enduring success stems from proven performance in diverse sectors, including automotive, pharmaceuticals, and water treatment, where it reduces wiring complexity and enables predictive maintenance through diagnostic capabilities.[4] Despite the rise of Ethernet-based successors like PROFINET, PROFIBUS remains integral to legacy and hybrid systems, underscoring its foundational role in modern industrial communication.[7]History
Origins
In the late 1980s, the industrial automation sector faced challenges from a proliferation of proprietary fieldbus systems, prompting the German Federal Ministry for Research and Technology (BMFT, now BMBF) to initiate a project in 1987 aimed at developing a unified, open fieldbus standard to enhance interoperability across diverse automation environments.[8][2] This effort culminated in the "Field Bus" collaboration project, which brought together 18 companies and institutes, including prominent German firms such as Siemens, Bosch, and Klöckner-Moeller (now Eaton), to design an accessible communication protocol for both process and factory automation applications.[8] The project emphasized creating a vendor-independent solution that could replace fragmented proprietary networks, fostering broader adoption in manufacturing and control systems.[2] The first PROFIBUS specification was published in 1989 as DIN V 19245, marking the formal introduction of the protocol with a primary focus on enabling seamless data exchange and interoperability among sensors, actuators, and controllers in industrial settings.[8] This standard laid the groundwork for open communication, addressing the need for standardized messaging in field-level devices without relying on closed vendor ecosystems.[2] Siemens quickly adopted PROFIBUS for integration into its SIMATIC programmable logic controller (PLC) systems, leveraging the protocol to streamline factory automation and demonstrate its practical viability in real-world deployments.[8] This early endorsement by a leading automation provider helped propel initial market acceptance and set the stage for subsequent variants tailored to specific applications.[2]Development and Milestones
Following its initial specification in 1989, Profibus saw significant advancements in the early 1990s with the introduction of Profibus DP in 1993, a variant optimized for high-speed communication in factory automation environments, enabling efficient decentralized control of peripherals.[2] This development addressed the need for faster data exchange in discrete manufacturing, building on the core protocol to support real-time operations.[8] In 1996, Profibus PA was launched to meet the demands of process industries, incorporating intrinsic safety features compliant with IEC 61158-2 for hazardous environments, thus extending Profibus applicability to chemical, oil, and pharmaceutical sectors.[2] By 1996, Profibus was incorporated into the European fieldbus standard EN 50170, which harmonized multiple protocols and facilitated wider adoption across Europe by providing a unified framework for interoperability and certification.[8] The early 2000s marked organizational evolution, with the PROFIBUS Nutzerorganisation (PNO) integrating PROFINET activities in 2003, leading to the formal renaming of the umbrella organization to PROFIBUS & PROFINET International (PI) in 2006 to reflect its expanded scope in industrial communications.[2] During the 2010s, Profibus achieved key integrations, including standardized interfacing with IO-Link in 2007 for seamless sensor-actuator connectivity and the launch of omlox in 2020 under PI for real-time localization, enhancing device-level data exchange and spatial tracking in automation systems.[9][10] By 2020, the cumulative installed base of Profibus and related PI technologies exceeded 100 million nodes globally, underscoring its enduring impact.[11] In 2024, PI celebrated 35 years since the 1989 founding of PNO, highlighting Profibus's sustained relevance amid the shift toward Ethernet-based systems, with PI surveys reporting 1.5 million new Profibus nodes installed in 2023 alone—a figure that included 0.9 million in process automation—demonstrating continued growth and adaptation. In 2024, 1.1 million new Profibus devices were installed, including 0.8 million in process automation.[7][12][6]Technical Architecture
Physical Layer
The physical layer of PROFIBUS, corresponding to OSI Layer 1, defines the hardware and transmission fundamentals for reliable communication in industrial environments, supporting multiple transmission technologies to accommodate diverse applications such as factory automation and process control.[13] These include RS-485 for high-speed multidrop networks, Manchester Bus Powered (MBP) for process automation with integrated power delivery, and fiber optics for extended reach and electromagnetic noise immunity.[4] RS-485 serves as the primary transmission technology for PROFIBUS DP, enabling multidrop, half-duplex communication over twisted-pair copper cabling with differential signaling.[14] It employs Non-Return-to-Zero (NRZ) encoding and supports baud rates ranging from 9.6 kbps to 12 Mbps, with maximum segment lengths decreasing at higher speeds due to signal attenuation and capacitance limits.[15] For example, at 9.6 kbps, distances up to 1200 m are achievable, while at 12 Mbps, the limit drops to 100 m.[16]| Baud Rate (kbps) | Maximum Segment Length (m) |
|---|---|
| 9.6 | 1200 |
| 19.2 | 1200 |
| 45.45 | 1200 |
| 93.75 | 1200 |
| 187.5 | 1000 |
| 500 | 400 |
| 1500 | 200 |
| 3000 | 100 |
| 6000 | 100 |
| 12000 | 100 |
Data Link Layer
The Data Link Layer of PROFIBUS, known as the Fieldbus Data Link (FDL) protocol, manages medium access control and reliable frame transmission in accordance with IEC 61158-6. It employs a hybrid access method combining master-slave polling with token passing to handle bus arbitration, ensuring deterministic and collision-free communication on shared media. In single-master configurations, the master polls slaves sequentially without token exchange, while multi-master setups form a logical ring where active masters circulate a token to gain exclusive transmission rights, preventing simultaneous access and maintaining order. The token passes in ascending address order among masters (addresses 0-127), with each master holding it for a configurable rotation time before passing it to the next, as defined by the medium access control (MAC) sublayer per DIN 19245 Part 1. This mechanism supports up to 126 devices, prioritizing real-time performance in industrial environments.[20][21][22] FDL defines several frame types to accommodate different communication needs: no-data frames for token-only transfers or status requests, variable-length frames supporting up to 244 bytes of user data for flexible exchanges, fixed-length frames limited to 8 bytes for efficient short transfers, token frames for passing bus control, and brief acknowledgment frames without start delimiters for quick confirmations. All frames follow a structured format starting with a 1-byte start delimiter (SD) to identify the type—such as 0x10 for no-data, 0x68 for variable-length, 0xA2 for fixed-length, or 0xDC for tokens—followed by length indicators. The length field (LE) specifies the byte count from destination address (DA) through the protocol data unit (PDU), while the length-variation field (LEr) repeats this value for redundancy and error checking. Subsequent fields include the 1-byte control or function code (FC or C) indicating frame purpose (e.g., request/response), 1-byte DA and source address (SA) for 8-bit station addressing (0-127, with 126 for broadcast), optional PDU containing data or service-specific elements like DSADR (destination station address repeat), a 1-byte frame check sequence (FCS) for integrity, and a 1-byte end delimiter (ED, typically 0x16). Transmission occurs in 11-bit characters (8 data bits, even parity, 1 start/stop bit) at rates up to 12 Mbps.[22][20][21] Service Access Points (SAPs) in FDL, denoted as DSAP (destination SAP) and SSAP (source SAP), provide logical endpoints for routing frames to specific application services within a device, using values from 0-63 or a default (0xFF). These 1-byte fields follow the FC in variable- and fixed-length frames, enabling multiplexed access to multiple services (e.g., SAP 61 for parameter setting) without altering the underlying station addresses. Error detection combines even parity bits per character with the FCS, computed as an 8-bit block check character (sum of bytes from DA to PDU modulo 256, ensuring Hamming distance HD=4 equivalent to CRC-16 protection for short frames), and delimiters to detect framing errors. Synchronization relies on a preamble of at least 33 logical '1' bits (SYN) before the SD, while collision avoidance is inherent to the token mechanism, as only the token holder transmits; any detected collision increments a counter for network diagnostics. Variable interframe times, governed by parameters like minimum/maximum station delay (min/max TSDR) and quiet time (TQUI), ensure proper spacing—typically 33 bit times minimum between frames—to allow bus settling and slave response timing, with the master enforcing gaps via configurable slot times (TSL).[22][20][21]| Frame Field | Size (bytes) | Description |
|---|---|---|
| SD (Start Delimiter) | 1 | Identifies frame type (e.g., 0x68 for variable-length) |
| LE (Length) | 1 | Total length of header + PDU |
| LEr (Length Variation) | 1 | Redundant copy of LE for error detection |
| FC/C (Control/Function Code) | 1 | Specifies service or response type |
| DA (Destination Address) | 1 | Target station (0-127 or 126 for broadcast) |
| SA (Source Address) | 1 | Originating station |
| DSAP/SSAP (Service Access Points) | 1 each (optional) | Routing to application services |
| PDU/Data (including DSADR if needed) | Variable (0-244) | User or protocol data |
| FCS (Frame Check Sequence) | 1 | Checksum (modulo 256 sum) + parity |
| ED (End Delimiter) | 1 | Marks frame end (0x16) |