VEGA VEGACOM 557 Modbus protocol - Manual (Page 30)

30 VEGACOM 557 Modbus
on
PC
VEGALOG
571
!
4.3 Measured value image when
connected to LOGBUS
The addressing of the measured values for
Modbus systems is "word orientated“. In
VEGACOM 557 a meas. value is represented
by two words, the first word includes the real
meas. value, the next higher word the re-
spective status information. In the standard,
the designation “register word” is also used
instead of the term “word”. The addressing is
either made via existing library enquiries of a
PLC (e.g. Modicon) or by direct generation of
Modbus telegrams.
Measured value image when connecting to VEGALOG
571
DCS output 1
DCS output 2
DCS output 3
DCS output 255
Meas.
value
z
Meas.
value
x
Meas.
value
y
Examples of valid register word addresses
are shown in the following demonstration.
Especially when using Modicon, make sure
that the register address for the library en-
quiry is increased by 1 with respect to the
transmitted address on the Modbus.
VEGALOG 571 can administrate up to 255
measurement loops. For transmission of
measured values from a measurement loop,
VEGALOG makes up to 255 DCS outputs
available.
One or several DCS outputs with any index
can be allocated to these measurement
loops. The configuration of VEGALOG 571 is
made with the VEGA adjustment software
VVO. You define, via the selected PC/DCS
output, where the respective measured val-
ues can be collected within the intermediate
storage in VEGACOM 557.
Note:
When addressing register words, all ad-
dresses between 0 and 65 535 can be used
with VEGACOM 557. When accessing the
intermediate storage, VEGACOM 557 gener-
ally uses only the last 3 digits of the address.
This results in the following conversion table:
Register Register Register
address in address on address in
Modicon Modbus VEGACOM
557
30 001 30 000 000
30 017 30 016 016
34 001 34 000 000
34 017 34 016 016
Data image in VEGACOM 557