Setting Up A Profibus Network; Network Structure - Omron GRT1 - 27-11-2006 Operation Manual

Setting up a PROFIBUS Network

2-4

Setting up a PROFIBUS Network

2-4-1

Network Structure

Communication Medium
Linear Bus Topology
Repeaters
Termination
Tree Topology
24
The PROFIBUS standard defines the use of EIA RS-485 as the main commu-
nication transport medium. The PROFIBUS DP Master Unit is designed to
interface directly to this type of medium. This section will discuss the setup of
networks based on this medium.
Note The other communication medium specified for PROFIBUS is optical fibre.
The PROFIBUS DP Master Units does not provide a direct interface to this
type of medium. However, by using third party couplers an interface between
EIA RS-485 and optical fibre networks can be made.
PROFIBUS DP defines the use of the Linear Bus Network Topology. The Bus
must be terminated at both ends, and must not contain network branches.
The total cable length of the bus depends on the cable and the selected baud
rate. Also, RS-485 specifies a maximum of up to 32 devices - master and
slave devices - per line segment. If more than 32 devices are to be con-
nected, or if the total length of the segment must be extended beyond its max-
imum, repeaters must be used to link the separate segments.
Note Repeaters are devices which connect two segments. They do not have a
device address of their own, but they do count in the total number of devices
in a segment.
A maximum of up to three repeaters between two devices in a network can be
used, i.e. a network can consist of up to 4 segments. The maximum number
of PROFIBUS devices in such a network is then 122. The figure below shows
an example of a two-segment network.
OMRON
SYSMAC CS1G
P R O G R A MMA B LE
C O N T R O LLE R
Station 1
Station 2
Termination
Station 63
The use of repeaters allows the extension of three or more Linear Bus seg-
ments into a Tree topology. In a tree topology more than three repeaters are
allowed, provided that there are no more than three repeaters between any
two devices in the network. The following figure presents an example of a net-
work with more than three segments and repeaters.
Termination
Station 3 Station 31
Station 33 Station 32
Section 2-4
Termination
Repeater