Omron SYSMAC CS Series Operation Manual page 24

Overview of PROFIBUS
PROFIBUS DP
OSI Layer 1, 2 and User
Interface
OSI Layer 1: Transmission
Medium
RS-485 Technology
RS-485 Transmission
Speed
Cable length
.
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
In the rest of this manual, only PROFIBUS DP is considered.
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.
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.
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.
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.
Baud rate (kbit/s)
9.6
19.2
45.45
93.75
187.5
500
1500
3000
6000
12000
The maximum cable length values depend on the transmission speed and are
based on type-A cable (see Cable Type on page 39). 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 Basic Functions
NOT DEFINED
Fieldbus Data Link (FDL)
RS485 / Fibre Optics
Distance / segment (m)
1200
1200
1200
1200
1000
400
200
100
100
100
Section 1-1
DP-Extensions
3