3
Overview of PROFIBUS
Section 1-1
PROFIBUS DP
In the rest of this manual, only PROFIBUS DP is considered.
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 devices or step-by-step commissioning of the
system without influencing the other devices. Later expansions have no effect
on devices 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 when the system is commissioned.
Cable length
The maximum cable length values depend on the transmission speed. The
length can be increased by the use of repeaters. However, it is not recom-
mended 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