Omron GRT1 - 27-11-2006 Operation Manual page 91

PROFIBUS Technology
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 trans-
mission. 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 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.
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 commis-
sioning 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
The maximum cable length values depend on the transmission speed and are based on type-A cable (see
Cable Type on page 25). 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.
A-3 Device Types
PROFIBUS distinguishes between master devices and slave devices.
Master devices determine the data communication on the bus. A Master can send messages without an exter-
nal request, as long as it holds the bus access right (the token). Masters are also referred to as active devices
in the PROFIBUS standard.
There are two types of master devices.
• A PROFIBUS DP Class 1 Master (DPM1) device is a central controller, which exchanges information with
the decentralized devices (i.e. DP slaves) within a specified message cycle.
• PROFIBUS DP class 2 Master (DPM2) devices are programmers, configuration devices or operator pan-
els. They are used during commissioning, for configuration of the DP system, or for operation and monitor-
ing purposes.
Slave devices are peripheral devices. Typical slave devices include input/output devices, valves, drives, and
measuring transmitters. They do not have bus access rights and they can only acknowledge received mes-
sages or send messages to the master when requested to do so. Slave devices are also called passive
devices.
The GRT1-PRT is a PROFIBUS DP Slave device.
To enable the exchange of devices from different vendors, the user data has to have the same format. The
PROFIBUS DP protocol does not define the format of user data, it is only responsible for the transmission of
this data. The format of user data may be defined in so called profiles. Profiles can reduce engineering costs
since the meaning of application-related parameters is specified precisely. Profiles have been defined for spe-
cific areas like drive technology, encoders, and for sensors / actuators.
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Distance / segment (m)
1200
1200
1200
1200
1000
Baud rate (kbit/s)
500
1500
3000
6000
12000
Appendix A
Distance / segment (m)
400
200
100
100
100