Fieldbus Protocols Explained: A Practical Overview for Industrial Applications (Part 2)
In Part 1, we explored Modbus and Foundation Fieldbus (FF)—two widely used protocols in process and factory automation. In this second installment, we take a closer look at PROFIBUS and CAN Bus, which are essential to real-time industrial control and embedded systems.
PROFIBUS: Process Field Bus
Background and Standardization
PROFIBUS (Process Field Bus) was developed in Germany in the early 1990s under DIN 19245 and quickly became a cornerstone of European industrial automation. By 1996, it was standardized as EN 50170, ensuring widespread adoption across the European Union.
Today, PROFIBUS is a dominant communication standard in:
- Automotive manufacturing
- Machine building
- Food & beverage processing
- Public transportation systems
- Environmental and utility engineering
Key Features of PROFIBUS
| Specification | Details |
|---|---|
| Data Rate | From 9.6 kbps to 12 Mbps |
| Max Nodes | Up to 127 devices (expandable with repeaters) |
| Max Data Length | 244 bytes typical, 255 bytes max |
| Physical Medium | Twisted pair (shielded/unshielded) or fiber optics |
| Topology Options | Line, tree, or bus |
| Cable Length | Up to 9.6 km (twisted pair); 90 km (fiber optics) |
Transmission Profiles
PROFIBUS-DP (Decentralized Peripherals):
High-speed cyclic communication for real-time field device control.
PROFIBUS-FMS (Fieldbus Message Specification):
Supports acyclic data and complex messaging for supervisory systems.
PROFIBUS-PA (Process Automation):
Based on IEC 61158-2, tailored for hazardous and process environments; supports intrinsic safety.
Network Access Control
- Token passing among masters.
- Master-slave protocol for communication between controllers and devices.
Application Layers
| Layer | Typical Use |
|---|---|
| Field Level | Real-time control of sensors, actuators, drives |
| Cell Level | Coordination of production lines using FMS |
| Plant Level | Enterprise integration for data monitoring and analytics |
CAN Bus: Controller Area Network
Origins and Evolution
CAN Bus was originally developed by BOSCH in the 1980s to simplify in-vehicle communication. It replaced bulky wiring harnesses with a robust, efficient networked system. Today, CAN is widely adopted in:
- Automotive systems
- Industrial automation
- Medical equipment
- Agricultural machinery
- Elevators and HVAC systems
It is standardized as:
- ISO 11898 – High-speed CAN (up to 1 Mbps)
- ISO 11519 – Low-speed, fault-tolerant CAN
Technical Highlights of CAN Bus
| Feature | Specification |
|---|---|
| Physical Medium | Twisted pair |
| Data Rate | Up to 1 Mbps (40 m); 50 kbps for long-distance (up to 10 km) |
| Node Capacity | Up to 110 nodes |
| Frame Size | Max 8 bytes per data frame |
| Arbitration | Priority-based access—higher-priority messages always succeed |
Application Scenarios
▸ Industrial Automation
Used in PLC networks, robotics, and embedded control systems with CANopen or DeviceNet protocols layered on top.
▸ Automotive Electronics
CAN is the backbone for Engine Control Units (ECUs) managing:
- Engine functions
- Anti-lock braking (ABS)
- Airbags
- Power steering
- Transmission systems
Often used alongside:
- LIN (Local Interconnect Network) – For door modules, windows, etc.
- MOST (Media Oriented Systems Transport) – For infotainment and multimedia.
Safety & Real-Time Control
CAN Bus is ideal for real-time data exchange and fail-safe applications. For example:
- Auto-locking doors at high speed
- Crash-triggered emergency unlock
- Redundant safety monitoring in industrial environments
Its non-destructive arbitration and low latency make it suitable for mission-critical systems.
Summary Comparison
| Protocol | Max Speed | Max Devices | Topology | Best For |
|---|---|---|---|---|
| Modbus | 100 Mbps (Ethernet) | 247 | Bus | Simplicity, legacy systems |
| FF (H1/HSE) | 31.25 kbps / 100 Mbps | 32 per segment | Bus/Star/Tree | Process automation, distributed control |
| PROFIBUS | 12 Mbps | 127 | Line/Bus/Tree | High-speed factory automation |
| CAN Bus | 1 Mbps | ~110 | Bus | Embedded systems, automotive control |
What’s Next?
In the final part of this series, we’ll provide a fieldbus selection guide, helping you choose the right protocol based on your application requirements, infrastructure constraints, and future scalability.
Contact Our Technical Experts
Post time: May-19-2025