Omron CJ1W-PRT21 Operation Manual page 22

Protocol architecture
Layer 1, 2 and user
interface
Transmission medium
High-speed, inexpensive
Easy installation
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
PROFIBUS-DP uses layers 1 and 2, and the user interface. Layers 3 to 7 are
not defined. 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 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. 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 per-
mits 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. 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 3-3-1
Fieldbus cabling ). The specified cable lengths are based on type-A cable (see
3-3-1 Fieldbus cabling ). The length can be increased by the use of repeaters.
The use of more than 3 repeaters in series is not recommended.
DP-Profiles
DP Basic Functions
NOT DEFINED
Fieldbus Data Link (FDL)
RS-485 / Fibre Optics
Section 1-2
DP-Extensions
3