5.4 Cyclic Data Transfer (Data_Exchange)
With PROFIBUS-PA, the cyclic transmission of analog values to the process control
system uses data blocks with a length of 5 bytes. The measured value is portrayed in
the first 4 bytes in the form of floating comma numbers according to the IEEE stand-
ard (see page 22). The 5th byte contains standardized status information which
belongs to the instrument (see page 22).
PLC → Prowirl 77 (Output data)
Index
output
data
Data item Access Data format/remarks Factory
setting
(unit)
0 control write With every transition of this byte from 0 to
another number, a binary control can be
performed with the cyclic service. A transition
from any bit pattern to 0 has no effect.
0 → 1: reset totalizer
0 → 2... 255: reserved
–
Prowirl 77 → PLC (Input data)
Index
output
data
Data item Access Data format/remarks Factory
setting
(unit)
0, 1, 2, 3 flow
(volume/time)
read 32-Bit floating point number (IEEE-754)
see page 22
dm
3
/s
4 status flow read see status codes page 22 –
5, 6, 7, 8 totalizer
(volume)
read 32-Bit floating point number (IEEE-754) dm
3
9 status totalizer read see status codes page 22 –
If not all outputs of Prowirl 77 are required, single data blocks can be eliminated from
the cyclic telegram using the device configuration from the PLC software. Only data
blocks which are needed in the system should be activated, thereby improving the
throughput of a PROFIBUS-PA system.
In Prowirl 77, three data blocks can be activated for cyclic data exchange. The follow-
ing table shows the necessary configuration data in extended format (h means that
the number is a hexadecimal number).
Byte Data item Access GSD
block description
Configuration data
(depending on
PROFIBUS master)
0...4 flow + status read Flow Rate Block 42h, 84h, 08h, 05h
5...9 totalizer + status read Total Volume Block 42h, 84h, 08h, 05h
0 control write Total Volume Reset 20h
The identification code 94h can be used for PROFIBUS masters which do not support
the extended format. However, the extended format is preferable since it contains
additional information for interpreting the data.
5 Communication Prowirl 77 PROFIBUS-PA
20 Endress+Hauser
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