Siemens Simovert Masterdrives Compendium page 333

09.2008
8.2.2 Description of the CBP's functions on the PROFIBUS-DP
Definition
Protocol
architecture
Transmission
equipment
Bus-access
procedure
Siemens AG 6SE7087-6QX70 (Version AK)
SIMOVERT MASTERDRIVES
PROFIBUS is an international, open field bus standard with a wide scope
of application in production and process automation. Neutrality and
openness are guaranteed by international standards EN 50170 and IEC
61158.
The PROFIBUS-DP enables very fast, time-critical transfer of data on the
field level.
With the PROFIBUS, a distinction is made between masters and slaves.
♦ Masters determine data traffic on the bus and are also designated in
the literature as active nodes.
There are two classes of master:
• DP-Master Class 1 (DPM1):
These are central stations (e.g. SIMATIC S5, S7 and
SIMADYN D) which exchange information with the slaves in
defined communications cycles.
• DP-Master Class 2 (DPM2):
Units of this type are programming units, planning units or control
and monitoring units which are used for configuring, starting up or
monitoring systems in operation.
♦ Slaves (e.g. CBP, CB15 etc.) can only acknowledge the messages
they receive or transfer messages to a master when the latter
requests a slave to do so. Slaves are also designated as passive
nodes.
The protocol architecture of the PROFIBUS-DP is oriented to the OSI
(Open System Interconnection) reference model in accordance with the
international standard, ISO 7498, and uses layers 1 and 2 as well as the
user interface.
When transmission equipment is being selected, criteria such as high
transmission speed and simple, inexpensive wiring and cabling is of
primary importance. PROFIBUS supports transmission according to
RS485 and also transmission by means of fiber-optic cable.
The transmission speed can be selected between 9.6 kbaud and 12
Mbaud. The same speed is specified for all units on the bus when the
system is started up for the first time.
The PROFIBUS works according to the token-passing procedure, i.e. the
masters become token holders for a defined time window in a logical
ring. Within this time window, the master can communicate with other
masters. Alternatively, it can communicate with slaves by using a lower-
level master-slave procedure.
The PROFIBUS-DP mainly uses the master-slave method and data is
usually exchanged with the drives cyclically.
Compendium Motion Control
Communication / PROFIBUS
8.2-3