VEGA Modbus-TCP, ASCII protocol - Manual (Page 3)

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1 Function as Modbus-TCP server
Modbus-TCP, ASCII protocol • VEGAMET 391/624/625, VEGASCAN 693, PLICSRADIO C62
30768-EN-130701
1 Function as Modbus-TCP server
1.1 Modbus-TCP - general description
VEGAMET 391/624/625, VEGASCAN 693 and PLICSRADIO C62
signal conditioning instruments work as Modbus-TCP servers and
make the existing PC/DCS values and relay switching conditions
available in a temporary storage for collection via Modbus-TCP.
The instruments comply with the "Open Modbus-TCP-Specification"
Release 1.0 from Schneider Electric. This standard is supported by
many process control systems, remote IOs, visualisation programs
and OPC servers. Communication is carried out via Port 502.
Beside the PC/DCS values, the switching conditions of the relay
outputs can also be queried.
The enquiry of the PC/DCS values and relay values is made via the
appropriate function code (see also Modbus specification).
•
Function code 01: Read Coil Status (enquiry of the relay values)
•
Function code 02: Read Input Status (enquiry of the relay values)
•
Function code 03: Read Holding Registers (enquiry of the PC/
DCS values)
•
Function code 04: Read Input Registers (enquiry of the PC/DCS
values)
These function codes are normally available as library enquiries in the
PLC (e.g. Modicon).
VEGAMET 391/624/625 and PLICSRADIO C62 can provide up to
six PC/DCS outputs, VEGASCAN 693 up to 30. Further relay values
also exist (fail safe relay/operating relay, depending on the instrument
type).
Via the selected PC/DCS output you define where the respective
measured values can be picked up in the temporary memory. The
configuration of the PC/DCS outputs is carried out via PACTware/
DTM.
1.2 Filing of the measured value as 2 byte short
The addressing of the PC/DCS values for Modbus systems is carried
out "Word-orientated". In the temporary memory, a PC/DCS value is
represented by two words. The first word contains the actual PC/DCS
value, the next higher word the corresponding status information. In
the specification, the term register word is also used instead of word.
The filing of measured values in the temporary memory is always
sorted according to PC/DCS output number. The following chart
shows the addressing of the temporary memory via Modbus.
Register address in
Modicon
Temporary memory of VEGAMET/PLICSRADIO
(1 word = 2 byte)
30001 PC/DCS output 1: Measured value
30002 PC/DCS output 1: Status
30003 PC/DCS output 2: Measured value
PC/DCS output