VEGA VEGACOM 557 Modbus protocol - Manual (Page 35)

VEGACOM 557 Modbus 35
High-Byte Low-Byte Unit Status
Meas. value Add. info
DCS value
Octet 1 Octet 2 Octet 3 Octet 4
Format for the transfer of measured values
5.3 Format for the transfer of meas-
ured values
Measured values and DCS values
The measured values of the VEGA process-
ing systems (VEGAMET or VEGALOG) con-
nected to VEGACOM 557 are reproduced at
the input registers of Modicon 584 in the way
described in chapter 4.1 and 4.3. They are
available in VEGACOM 557 as so called DCS
values.
A DCS value covers two register addresses,
it consists therefore of 2 double words, i.e. 4
Byte.
A complete overview of the image of the DCS
values in the input registers of Modicon and
alternative addressing schemes can be
found in supplement A of this manual.
Structure of a measured value
Measured values of the VEGALOG or VEGA-
MET processing systems are transferred to
VEGACOM 557 as signed data containing 2
octets. This means that the value range com-
prises max. +32768 to -32767.
Structure of a DCS value
An individual DCS value in VEGACOM 557
consists of 4 octets and is composed as
follows:
The real meas. value has a length of 2 octets
and is signed, this means that the value
range is between +32768 and -32767.
In addition to the meas. value, VEGACOM
557 provides one octet per DCS value for
information on the measuring unit and another
octet for information on the current status of
the measured value.
The octet for the unit or measurement pres-
ently unused - it is always filled with the value
zero.
The status describes the condition of the two
respective meas. value octets. The content of
the meas. value octet is only valid when the
respective status has the value zero.
If there is a status value unequal zero, the
status value and the respective value in the
measured value field must be taken into
account for detailed error diagnostics. The
following list explains the possible errors:
Status Meas. value Meaning
0x00 0xXXXX valid measured value
0x01 0xXXXX simulated meas. value
(only on VEGAMET 509
and 512)
0x80 0xXXXX old meas. value (prob-
ably connection sepa-
rated)
0xFE 0x0000 there is no meas. value
available (not config-
ured)
0xFF 0xFFFF there is no VEGAMET or
VEGALOG connected
0xFF 0x00XX failure message of an
individual meas. loop
XX = error type
0xFF 0x8000 failure message of an
individual meas. loop
Error type not defined