NORD Drivesystems BU0220 - Manual (Page 84)

PROFIBUS DP – Supplementary manualfor NORD Frequency Inverter SK 2xxE
84 Subject to technical amendments BU 0220 GB-0912
8.3 PROFIBUS DP 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 is standardised in the international standard IEC 61158.
It 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 variety of field devices can therefore be easily interlinked. In case of failure of
individual field devices, data transfer to the remaining bus subscribers continues uninterrupted.
The system configuration or bus structure can be implemented both as a mono-master system (only one
master) and as a multi-master system (several masters).
8.3.1 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 1 Physical layer defines the hardware, coding, speed etc. of data transfer

Layer 2 Connection layer describes the bus access procedure including data
security, i.e. it defines the physics of transfer

Layer 7 Application layer defines the interface to the application program with the
application-orientated commands.
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.