BECKHOFF BC3150 - Manual (Page 83)

Safety Instructions
Fieldbus Components 81
6. PROFIBUS
System Introduction
Fieldbus Overview
Profibus is a manufacturer - independent, open fieldbus standard with a wide range of applications in manufacturing
and process automation. Manufacturer-independence and openness are guaranteed by the International standards
EN 50170 and EN 50254. Profibus allows devices from different manufacturers to communicate without the need for
specially adapted interfaces. Profibus is suitable both for fast, time-critical applications and for complex
communication tasks.
Profibus offers communication protocols of different functional levels: DP and FMS. According to the application, RS-
485, IEC 1158-2 or optical fiber are available as transmission techniques.
Profibus specifies the technical features of a serial fieldbus system with which distributed digital automation devices
can be networked together, from the field level up to the cell level. Profibus is a multi-master system, and therefore
permits common operation of a number of automation, engineering or visualization systems with their distributed
peripheral devices on one bus.
Profibus distinguishes the following device types:
Master devices determine the data traffic on the bus. A master may transmit messages without having received an
external request when it is in possession of the bus access authorization (token). Masters are also referred to as
active devices.
Slave devices are peripheral devices such as input/output devices, valves, drives, measuring transducers and the
Beckhoff Profibus slaves from the BK3xx0, BC3xx0, IPxxxx-B310, IL230x-B310 and IL230x-C310 series. They do not
receive any bus access authorization, so that they are only allowed to acknowledge messages that have been
received, or to send messages in response to a request from master. Slaves are referred to as passive devices. They
only require a small proportion of the bus protocol, which means that they can be implemented with little effort.
Profibus DP
Profibus DP is designed for efficient data exchange at the field level. The central automation devices such as
PLC/PCs or process control systems communicate here over a fast serial link with distributed field devices such as
I/O, drives, valves etc.. Data is primarily exchanged with these distributed devices cyclically. The communication
functions required for this are specified by the basic DP functions in accordance with EN 50170.
In addition to these basic functions, Profibus DP also offers extended acyclic communication services for such
purposes as parameterization and other operations. These are also supported by the Beckhoff Profibus slaves of the
IPxxxx-B310, IL230x-B310 and IL230x-C310 series. A central controller (master) cyclically reads the input
information from the slaves, and writes the output information cyclically to the slaves. The bus cycle time here should
be shorter than the central automation system's program cycle time, which lies around 10 ms in many applications.
A high data throughput is not in itself sufficient for successful use of a bus system. Ease of handling, good diagnostic
facilities and secure transmission technology are also of the utmost importance if the user’s demands are to be
satisfied. These properties are ideally combined in Profibus DP.
System configuration and device types
Profibus DP allows single master or multi-master systems to be implemented. This permits a high level of flexibility
in system configuration. A maximum of 126 devices (master or slaves) can be connected to one bus. A station
address between 0 and 99 can be chosen for the Beckhoff Profibus slaves from the IPxxxx-B310, IL230x- B310 and
IL230x-C310 series. The specifications for the system configuration contain the number of stations, the assignment of
the station addresses to the I/O addresses, data consistency of the I/O data and the format of the diagnostics
messages and the bus parameters being used. Every Profibus DP system consists of different device types.