7 Using the MODBUS output interface
7.1 General points
Whether it runs with XPR, with VIO or in stand-alone mode, MVX computes and
updates as often as possible a number of scalar levels (called “overall levels” or
“indicators”).
All these levels can be consulted using the dialogue function in MODBUS format.
The status of these indicators (OK, Alarm, etc.) is also available, along with their unit.
In any event, MVX is a MODBUS slave that answers requests issued by a Master.
This Master is usually a programmable automaton, a centralized management
system or a monitoring system.
7.2 Communication principles
Data in MODBUS format can be accessed:
Either using the RS485 connection on MVX: “Serial MODBUS”
Or using the Ethernet connection of MVX: “MODBUS-TCP”
7.2.1 Serial MODBUS with RS485 connection
The RS485 standard allows for the creation of a local network made up of a twisted
and shielded pair onto which up to 32 instruments can be connected.
In practice, one needs to connect one or several MVX instruments to a single
“master” instrument.
We recommend reading Chapter 3.9 of MVX installation manual P153.NUT.576
before achieving the physical connection of instruments.
It is possible to adjust RS485 configuration (baud rate, parity …) with CAST software.
Each MVX is assigned a MODBUS slave number ranging from 1 to 32. The
MODBUS slave address of each MVX is set from the ONEPROD NEST ANALYST
(XPR) software or from the OneProd CSM software.
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