PLX51-PBM
PROFIBUS DP
PROFIBUS DPV0/DPV1 Master or Slave to EtherNet/IP™ or Modbus® Gateway
User Manual
ProSoft Technology, Inc.
Page 190 of 196
10.1.3
PROFIBUS FMS
PROFIBUS FMS is the general-purpose solution for communication tasks at the cell
level. Powerful FMS services open up a wide range of applications and provide great
flexibility. PROFIBUS FMS can also be used for extensive and complex
communication tasks. This protocol is the first developed for PROFIBUS, but it is no
longer currently used.
PROFIBUS specifies the technical and functional characteristics of a serial fieldbus
system with which decentralized digital controllers can be networked together from
the field level to the cell level.
10.2
PROFIBUS Master and Slave
PROFIBUS distinguishes between master devices and slave devices.
Master devices
determine the data communication on the bus. A master can send
messages without an external request when it holds the bus access rights (the
token). Masters are also called '
active stations
' in the PROFIBUS protocol.
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 messages or send messages to the
master when requested to do so. Slaves are also called '
passive stations
'.
10.3
PROFIBUS Master Class 1 (DPM1) or class 2 (DPM2)
10.3.1
PROFIBUS DP Master class 1 (DPM1)
A class 1 master handles the normal communication or exchange of data with the
slaves assigned to it. This is typically a PLC.
It uses
cyclic communication
to exchange process data with its associated slaves.
The class 1 master sets the baud rate and the slave’s auto-detect this rate. Each
slave device is assigned to one master and only that master may write output data to
that slave. Other masters may read information from any slave but can only write
output data to their own assigned slaves.
10.3.2
PROFIBUS DP Master class 2 (DPM2)
A class 2 master is a special device primarily used for commissioning slaves and for
diagnostic purposes. This is typically a Supervisor. It uses
acyclic communication
over what is known as the
MS2 channel
. A DPM2 does not have to be permanently
connected to the bus system.
10.4
Cyclic Communication
The DP master class 1 cyclically exchanges data with all of the slaves assigned to it.
This service is configured. During the configuration process, master and slave
addresses are assigned, the bus parameters are defined, the types and numbers of
modules (in the case of modular slaves) are specified, user-selectable parameter
choices are made, etc.
Before data exchange can take place, the master will send parameterization and
configuration telegrams to all of its assigned slaves. These parameters and
configuration data are checked by the slaves. If both are valid, the master will initiate
cyclic I/O data communication with the slave devices.
