16
MOVITRAC
®
31.. PROFIBUS Fieldbus Interface
3
The PROFIBUS-DP
Interface
3
The PROFIBUS-DP Interface
PROFIBUS-DP (Decentralized Periphery) is the speed-optimized PROFIBUS option designed in par-
ticular for fast data exchange at the sensor/actuator level. DP is used by central automation sys-
tems (e.g. programmable logic controllers) to communicate with decentralized peripherals such as
sensors and actuators, among them inverters, via a fast serial link. Data exchange with these
decentralized units is mainly cyclic. The central control system sends new process output data to
all slaves in a message and reads in all process input data from the slaves (sensors, actuators) in
the same message.
The considerable increase in speed of PROFIBUS-DP compared to PROFIBUS-FMS is primarily due
to the fact that DP has no application layer (layer 7) and I/O data are transferred between the mas-
ter and a slave in a single message cycle. A maximum of 246 bytes of I/O data can be transferred
between the DP master and a DP slave. Normally, however, shorter data blocks (of up to 32 bytes)
are used to increase efficiency still further. Consequently, the exchange of data via PROFIBUS-DP
can be seen as a straight process communications procedure.
To enable the DP master to communicate with the DP slaves, it has to be given some important
information regarding the DP interface of the connected slave. In addition to data relating to the
type and amount of I/O data to be transferred, it also requires additional information regarding the
identity of each DP slave.
3 .1
Configuration of the DP Interface
To be able to define the type and amount of I/O data to be transferred, the DP master has to pass a
certain configuration to the inverter. The MOVITRAC
®
31.. inverter can generally be operated using
six different configurations. You have the option of only controlling the inverter by exchanging
process data, or, in addition to controlling the inverter via process data, of reading or writing
parameters using an additional parameter channel at the same time.
Fig. 11 provides a schematic representation of the exchange of data between the programmable
automation unit (DP master) and the MOVITRAC
®
31.. inverter (DP slave) using process data and
parameter channels.
00945AEN
Fig. 11: Communication via PROFIBUS-DP
MOVIT
RAC
E
Q
RUN
BUS
FAULT
841
FIELDBUS
Control Mode
Parameter channel
Parameter channel
Process data channel
Process data channel
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