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PROFIBUS
ISO/OSI model
At the moment, PROFIBUS DP is the Field bus most frequently used worldwide for industrial
applications. It is standardized under IEC 61158 together with other field bus protocols.
The definition of the PROFIBUS is based on the experience concerning data transmission collected
during long years.
One base is the ISO/OSI model (Open Systems Interconnection Reference Model). It is an open layer
model with 7 layers for the communication in information processing systems. The model describes
uniformed procedures and rules for the exchange of data.
Fieldbus systems normally use only three of the 7 layers:
ISO/OSI
Transmitting
CPU
Layer 7
Application
layer
...
...
Layer 2
Data-link
layer
Layer 1
Physical
layer
Transmission medium (physical)
As a result of the ISO/OSI layer model, each layer can be defined separately and (nearly) independent of
the other layers.
Indeed, it is possible and common to use conventional cables, but also optical fibers as physical layer for
the PROFIBUS DP or have a mixture of both in a single bus configuration.
For the application layer, there are also different versions possible, e.g. PROFIBUS DP-V0, PROFIBUS
DP-V1 but also others that are not regarded here.
____________________________________________________________________________________________________________
V2
AC500 Hardware
Receiving
CPU
Application
=
Interface to the application program (CPU) with
layer
application oriented commands (read, write)
...
Data-link
=
Access control (to the line), telegram (start,
layer
length,..), data security (e.g. CRC=Cyclic
Redundancy Code)
Physical
=
Definition of the medium (Twinax, optical fiber,
layer
..), coding ("1"=-4V), transmission speed (baud
rate)..
1-44
System data
AC500 / Issued: 05.2007
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