Raco Verbatim, Owner'S Manual

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MODBUS Interface
Verbatim Owner's Manual F-1
F
MODBUS Interface
This section covers the PLC specific functions of the Verbatim autodialer. It is
assumed the reader is already familiar with the basic operation of the Verbatim
autodialer. If this is not the case, please take the time now to review the
previous sections of this manual.
In the discussion that follows, there are many technical terms specific to PLC
operation which may be unfamiliar to those not experienced with PLCs. Please
refer to the Glossary section for definition of these terms.
F.1 Overview
The Verbatim autodialer allows direct connection to Programmable Logic
Controllers (PLCs) via a serial interface or other network connection. No direct
connections from PLC output points to the Verbatim input points are required in
order to monitor or annunciate for the PLC. Also, in most cases, no changes in
the PLC’s ladder logic program are required.
In addition, the autodialer allows connection to any non-PLC equipment
compatible with supported PLC network protocols. An example of this
application is a SCADA or DCS system running software configured with a
PLC network protocol driver module. The autodialer does not care if the
devices are a real PLC network or a computer mimicking a PLC network.
However, master/slave protocols will require the autodialer to assume the role
of master.
The Verbatim autodialer may read or write any data register within the PLC
network. The data registers accessed by the autodialer may be in a single PLC
or may be arbitrarily spread over a number of PLCs on the network.
Obviously, the number of data table locations in even a single PLC may number
into the thousands. To relieve the user of having to deal with a huge number of
precisely notated data table addresses, the autodialer uses the artifice of Remote
Channels (RCs). Simply stated, RCs are nothing more than a kind of speed-dial
number like you might set up on your telephone. Once the full number sequence
has been entered into memory, a shorter sequence of numbers may be used as
an abbreviation for the long sequence stored in memory.
Through the Verbatim autodialer, the user associates the address of a PLC data
register to a RC. Thereafter, the RC becomes a shorthand designation for that
data register’s address. Any register, whether digital, analog, or other
miscellaneous type, may be associated with an RC.