2 Nomenclature and Installation
2-8
CJ-series PROFIBUS Slave Unit Operation Manual for NJ-series CPU Unit (W510)
2-3
Network Installation
Communication Medium
The PROFIBUS standard defines the use of EIA RS-485 as the main communication transport
medium. The PROFIBUS Slave 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 fiber. The PROFIBUS
Slave 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 fiber networks can be
made.
Linear Bus Topology
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 connected or if the total
length of the segment must be extended beyond its maximum, 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.
Repeaters
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.
2-3-1
Network Structure
Station 2
Station 3
Station 31
Repeater
Station 63
Station 33
Station 32
Termination
Termination
Termination
Termination
OMRON
SYSMAC CS1G
P R O G R A MMA B LE
C O N T R O LLE R
Station 1
