PROFIBUS Overview
(1) PROFIBUS is an international, open, and vendor-independent fieldbus standard. It is widely applicable in manufacturing automation, process industry automation, and automation in other sectors such as buildings, transportation, and power.
(2) PROFIBUS comprises three compatible components: PROFIBUS-DP (Decentralized Periphery), PROFIBUS-PA (Process Automation), and PROFIBUS-FMS (Fieldbus Message Specification).
(3) PROFIBUS-DP: A high-speed, low-cost communication protocol for device-level control systems and distributed I/O communication. PROFIBUS-DP replaces conventional 24VDC or 4-20mA signal transmission.
(4) PROFIBUS-PA: Specifically designed for process automation, enabling sensors and actuators to be connected on a single bus with intrinsic safety specifications.
(5) PROFIBUS-FMS: Used for shop-floor monitoring networks, it is a token-based, real-time multi-master network.
(6) PROFIBUS is a fieldbus technology for shop-floor monitoring and data communication/control at the field device level in factory automation. It enables distributed digital control and field communication networks from the field device level to shop-floor monitoring, providing a viable solution for achieving comprehensive factory automation and intelligent field devices.
PROFIBUS Protocol Structure
The PROFIBUS protocol structure is based on the ISO 7498 international standard, using the Open System Interconnection (OSI) model as its reference framework. This model comprises seven layers, as illustrated below:
(1) PROFIBUS-DP: Defines the first, second, and user interfaces. Layers three through seven are not described. The user interface specifies application functions accessible to users, systems, and various devices, and details the device behavior of different PROFIBUS-DP devices.
(2) PROFIBUS-FMS: Defines Layers 1, 2, and 7. The application layer incorporates the Fieldbus Message Specification (FMS) and the Lower Layer Interface (LLI). FMS includes application protocols and provides users with a robust, widely selectable range of communication services. LLI coordinates different communication relationships and offers a device-independent Layer 2 access interface.
(3) PROFIBUS-PA: PA data transmission utilizes an extended PROFIBUS-DP protocol. Additionally, PA describes the PA conventions governing field device behavior. Based on the IEC 1158-2 standard, PA's transmission technology ensures intrinsic safety and enables power supply to field devices via the bus. PA networks can be extended over DP using connectors.
PROFIBUS Transmission Technology
PROFIBUS provides three data transmission types:
1. RS485 transmission for DP and FMS.
2. IEC 1158-2 transmission for PA.
3. Fiber optic transmission.