3 2
MOVITRAC
®
31.. PROFIBUS Fieldbus Interface
3
The PROFIBUS-DP
Interface
3 .7
Parameter setting via PROFIBUS-DP
The inverter parameters are read and written by the READ and WRITE services of the application
layer (layer 7). If there is no layer 7, as in the case of PROFIBUS-DP, a suitable application layer
must be emulated, i.e. mechanisms for setting the inverter parameters must be created.
3 .7.1
Structure of the Parameter Channel
The parameterizing of field units using fieldbus systems, which do not provide an application layer,
requires the emulation of the most important functions and services, such as READ and WRITE for
the reading and writing of parameters. In the case of PROFIBUS-DP, this requires a Parameter
Process Data Object (PPO) to be defined. This PPO is transferred cyclically and in addition to the
process data channel contains a parameter channel through which acyclic parameter values can be
transferred (Fig. 38).
00945AEN
Fig. 38: Parameter process data object for PROFIBUS-DP
Fig. 39 shows the structure of the parameter channel. It generally consists of a management byte,
an index word, a reserved byte and four data bytes.
00951AEN
Fig. 39: Structure of the parameter channel
Management of the Parameter Channel
The entire parameter adjustment procedure is co-ordinated using byte 0:
Management. This byte
makes important parameters, such as service identifier, data length, version and status, of the exe-
cuted service available. Fig. 40 shows that bits 0, 1 and 2 contain the service identifier, in other
words, they define which service is to be executed. Bit 3 is currently reserved and should generally
remain set to zero. Bit 4 and bit 5 contain the data length in bytes for the Write service, which in the
case of SEW inverters should normally be set to 4 bytes.
MOVIT
RAC
E
Q
RUN
BUS
FAULT
841
FIELDBUS
Control Mode
Parameter channel
Parameter channel
Process data channel
Process data channel
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Management
reserved
Parameter index
4-byte data
Management reserved
Index high
Index low
Data MSB
Data
Data
Data LSB
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