NORD Drivesystems BU0020 - Manual (Page 47)

5 PROFIBUS technology and protocol
BU 0020 GB-2612 47
5. PROFIBUS technology and protocol
The PROFIBUS (Process Field Bus) is the fastest standardised (open) bus system for field use. This
technology enables consistent communication down to the lowest field level and is widely used in
production, process and building automation systems. Profibus was developed by SIEMENS and the
Profibus users' organisation and was standardised in the international standard IEC 61158. Profibus is
a multi-master system and therefore enables the joint operation of several automation, engineering or
visualisation systems with decentralised peripheral devices on a common field bus. The protocol
describes the process rules for the transfer of data. The protocol specifies both the format of
messages as well as the flow of data in data transfer. A wide range of field devices can be networked
without problems, and in case of failure of individual field devices, data transfer to the remaining bus
participants continues without interruption.
The system configuration or bus structure can be planned and implemented both as a mono-master
system (only one master) and as a multi-master system (several masters).
Pos: 57 /Anleitungen/Bussysteme/4. Protokoll/Profibus [BU0020]Übersicht / Protokollarchitektur @ 1\mod_1335521150251_388.docx @ 24457 @ 2 @ 1
5.1 Overview /Protocol architecture
The ISO/OSI layer model describes the communication between the individual participants (slaves) of
a communication or automation system. Of the seven defined OSI layers, PROFIBUS uses layers 1, 2
and 7. PROFIBUS DP only uses layers 1 and 2 and the DP user interface.
Layer Type Meaning
1 Physical layer defines the hardware, coding, speed etc. of data transfer
2 Connection layer describes the bus access procedure including data security, i.e. it
defines the physics of transfer
7 Application layer defines the interface to the application program with the
application-orientated commands.
Table 7: ISO/OSI Layer model
Layer 2 of the ISO/OSI model includes
• the general format for data transfer telegrams
• the bus access mechanisms
• the security mechanisms
• the times to be complied with
• possible transfer services.
The user only has a slight influence on the design of layer 2, as almost all services are included in the
available PROFIBUS ASICs.
Pos: 58 /Anleitungen/Bussysteme/4. Protokoll/Profibus [BU0020]Gerätetypen PROFIBUS DP @ 1\mod_1335521632362_388.docx @ 24481 @ 2 @ 1
5.2 PROFIBUS DP device types
PROFIBUS DP is an acronym for "Process Field Bus for Decentralised Peripherals" i.e. for the simple,
rapid, cyclic and deterministic exchange of process data between a PROFIBUS master and the
assigned PROFIBUS slaves connected to the field bus. The exchange of process data takes place
between central automation devices such as PLCs, PCs or process control systems and decentralised
field devices such as drive units, valves, analysis devices and frequency inverters. Exchange of
process data is mainly carried out cyclically between the PROFIBUS participants (master ↔ slaves).
The DP communication protocol is categorised into three basic functions or performance levels, DP-
V0, DP-V1 and DP-V2.