3
Overview of PROFIBUS
Section 1-1
• Layer 7, the Application Layer of this model, defines the application func-
tions. This Layer is only applicable to PROFIBUS-FMS.
OSI Layer 1, 2 and user
interface
PROFIBUS-DP uses layers 1 and 2, and the user interface. Layers 3 to 7 are
not defined for PROFIBUS-DP. The User interface Layer defines the interface
functions for specific application areas, i.e. the PROFIBUS-DP basic functions
and communication profiles.This streamlined architecture ensures fast and
efficient data transmission. The application functions which are available to
the user, as well as the system and device behaviour of the various PROFI-
BUS-DP device types, are specified in the user interface.
OSI Layer 1: Transmission
medium
RS-485 transmission technology or fibre optics are available for transmission.
RS-485 transmission is the most frequently used transmission technology. Its
application area includes all areas in which high transmission speed and sim-
ple inexpensive installation are required. PROFIBUS modules are intercon-
nected by single twisted-pair shielded copper wires.
RS-485 technology The RS-485 transmission technology is very easy to handle. Installation of the
twisted pair cable does not require expert knowledge. The bus structure per-
mits addition and removal of stations or step-by-step commissioning of the
system without influencing the other stations. Later expansions have no effect
on stations which are already in operation.
RS-485 Transmission
speed
Transmission speeds between 9.6 kbit/s and 12 Mbit/s can be selected as
shown in the table below. One unique transmission speed must selected for
all devices on the bus (master and slave devices) when the system is com-
missioned
Cable length The maximum cable length values depend on the transmission speed and are
based on type-A cable (see
Cable Type
). The length can be increased by the
use of repeaters.However, it is not recommended to use more than three
repeaters in series in a PROFIBUS network.
DP-Profiles
DP-Extensions
User Interface Layer DP Basic Functions
(7) Application Layer
(6) Presentation Layer
(5) Session Layer NOT DEFINED
(4) Transport Layer
(3) Network Layer
(2) Data Link Layer Fieldbus Data Link (FDL)
(1) Physical Layer RS485 / Fibre Optics
Baud rate (kbit/s) Distance / segment (m)
9.6 1200
19.2 1200
45.45 1200
93.75 1200
187.5 1000
500 400
1500 200
3000 100
6000 100
12000 100
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