
Overview
1-6
SIMATIC 505 PROFIBUS-FMS CP User Manual
1.3 Network Overview
The
Process Field Bus (PROFIBUS) standard (EN 50 170, V
olume 2,
PROFIBUS) defines the physical and logical parameters of a bit-serial bus
network. PROFIBUS offers an interface for high-speed communications
with field devices, as well as exchange of complex data between master
stations. One objective of the standard is to create an open system that
enables networking of programmable logic controllers and field devices from
different vendors. This allows you to include in your system any device from
another vendor as long as the device conforms to the standard.
While PROFIBUS includes FMS and DP protocols, there is a universal set
of standard physical parameters for PROFIBUS networks, as listed in
T
able 1-1.
T
able 1-1
PROFIBUS Physical Parameters
Features Parameters
Access mode Token passing with underlying master/slave
Transmission rate
9.6 Kbaud to 12 Mbaud
Transmission medium
Electrical network: shielded two-wire cable
Optical network: fiber-optic cable (glass or plastic)
Maximum number of devices
per segment
32 (including repeater)
Maximum number of station
addresses per network
126 (not including repeaters)
Maximum cable length per
network
10 km for copper cable; more for fiber-optic cable
(see Siemens
SIMATIC NET Industrial
Communications Networks, Catalog IK 10).
Topology
Electrical network: line, tree
Optical network: ring, line, star
Protocols
PROFIBUS-FMS
PROFIBUS-DP
Data size that can be
transmitted in one message
1 to 244 bytes
The
PROFIBUS
Standard
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