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1-2
Section
Protocol architecture
3
1-2
Protocol architecture
The PROFIBUS-DP protocol architecture is oriented on the Open System
Interconnection (OSI) reference model in accordance with the international
standard ISO 7498.
DP-Profiles
DP-Extensions
User Interface Layer
DP Basic Functions
(7) Application Layer
(6) Presentation Layer
(5) Session Layer
NOT DEFINED
(4) Transport Layer
NOT DEFINED
(3) Network Layer
(2) Data Link Layer
Fieldbus Data Link (FDL)
(1) Physical Layer
RS-485 / Fibre Optics
OSI layer model of PROFIBUS-DP
PROFIBUS-DP uses layers 1 and 2, and the user interface. Layers 3 to 7 are not
defined.
Layer 1 (physical layer) defines the physical transmission characteristics.
Layer 2 (data link layer) defines the bus access protocol.
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 PROFIBUS-DP device types, are specified in
the user interface.
RS-485 transmission technology or fibre optics are defined as transmission
medium. RS-485 transmission is the most frequently used transmission
technology. Its application area includes all areas in which high transmission
speed and simple inexpensive installation are required. Twisted pair shielded
copper cable with one conductor pair is used.
The RS-485 transmission technology is very easy to handle. Installation of the
twisted pair cable does not require expert knowledge. The bus structure permits
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.
Various transmission speeds between 9.6 kbit/s and 12 Mbit/s can be selected.
One unique transmission speed is selected for all devices on the bus when the
system is commissioned.
The maximum cable length depends on the transmission speed (see section
2-3-1). The length can be increased by the use of repeaters. The use of more
than 3 repeaters in series is not recommended.
OSI
Layer 1, 2 and user
interface
Transmission medium
Easy installation
Cable length