Profibus Communication Protocol - Omron CJ1W-PRT21 Operation Manual

Precautions for Correct Use Precautions for Correct Use
It is not possible to exchange one of these family members by another family member. This will
cause faulty operation.
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PROFIBUS Communication Protocol

 OSI Reference Model ISO-7498
In general, the PROFIBUS communication protocol is based on the Open System Interconnection
(OSI) reference model in accordance with the international standard ISO-7498 (see the following
illustration). The model defines 7 layers of communication functions, three of which - layers 1, 2, and
7 - are used in PROFIBUS.
• Layer 1, the Physical Layer of this model, defines the physical transmission characteristics.
• Layer 2, the Data Link Layer of this model, defines the bus access protocol. This protocol also
includes data security and the handling of transmission protocols and telegrams.
• Layer 7, the Application Layer of this model, defines the application functions. This layer is
only applicable to PROFIBUS FMS.
User Interface Layer
(7) Application Layer
(6) Presentation Layer
(5) Session Layer
(4) Transport Layer
(3) Network Layer
(2) Data Link Layer
(1) Physical Layer
 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 PROFI-
BUS 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 behavior of the various PROFIBUS 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 simple inexpensive installation are required. PROFIBUS modules are
interconnected 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 permits 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.
CJ-series PROFIBUS Slave Unit Operation Manual for NJ-series CPU Unit (W510)
DP-Profiles
DP Basic Functions
NOT DEFINED
Fieldbus Data Link (FDL)
RS485 / Fibre Optics
1 Features and System Configuration
DP-Extensions
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