ILX56-PBS
PROFIBUS DP
ControlLogix® Platform
User Manual
Page 66 of 87
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.
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
'
PROFIBUS master class 1 (DPM1) or class 2 (DPM2)
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.
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.
