What is Profibus DP? An Introduction – 8500698

Introduction to Profibus DP

What is Profibus DP? An Introduction

What is Profibus DP?

Profibus was created in 1989 by the German government in cooperation with several manufacturers of automation equipment. It is a messaging format specifically designed for high-speed serial I/O in factory and building automation applications. It is an open standard and is recognized as the fastest FieldBus in operation today. It’s based on RS485 and the European EN50170 Electrical Specification. The DP suffix refers to “Decentralized Periphery;” which is used to describe distributed I/O devices connected via a fast serial data link with a central controller. To contrast, a programmable logic controller (PLC) normally has its input/output channels arranged centrally. By introducing a network bus between the main controller (master) and its I/O channels (slaves), we have decentralized the I/O.

Profibus is based on universal international sta,ndards. Further, it’s oriented to the OSI (Open System Interconnection) reference model per international standard ISO 7498. In this model, every layer handles precisely defined tasks:

  • Physical Layer/Layer 1:  defines the physical transmission characteristics
  • Data Link Layer/Layer 2:  defines the bus access protocol
  • Application Layer/Layer 7:  defines the application functions

Profibus DP uses only layers 1 & 2 of this model, plus the user interface. Layers 3 to 7 are not used.

What does a Profibus system use?

The Profibus system uses a bus master to poll slave devices, distributed in multi-drop fashion on an RS485 serial bus. A Profibus slave is any peripheral device; I/O transducer, valve, network drive, or other measuring device; which processes information, in addition to sending its output to the master. The slave forms a “passive station” on the network. It does not have bus access rights and can only acknowledge received messages; or send response messages to the master upon request. It’s important to note that all Profibus slaves have the same priority. Additionally, all network communication originates from the master. Acromag I/O modules form intelligent slave devices.

Acromag modules implement the Profibus protocol via an industry-standard SPC3 ASIC from Siemens. This ASIC acts like a RAM or UART chip to the internal microcontroller; it completely handles the requirements of the protocol standard. The ASIC will then transfer network data to and from the microcontroller; followed by automatically providing the response to the bus according to the Profibus specification.

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