Modbus Applications; What Is Modbus Tcp/Ip; Protocol Description - ICP DAS USA WF-2000 Series User Manual

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5. Modbus Applications

The WF-2000 is a Modbus device that allows you to access
terminals data via Wi-Fi and communicates using a master-slave
technique in which only one device (the master) can initiate transactions
(called queries). The other devices (slaves) respond by supplying the
requested data to the master, or by taking the action requested in the
query.
Most SCADA Supervisor Control And Data Acquisition and HMI
software can easily integrate serial devices via the Modbus protocol,
such as Citect, ICONICS, iFIX, InduSoft, Intouch, Entivity Studio, Entivity
Live, Entivity VLC, Trace Mode, Wizcon, Wonderware, etc.

5.1 What is Modbus TCP/IP?

Modbus is a communication protocol developed by Modicon in 1979.
Different versions of Modbus used today include Modbus RTU
(based on serial communication like RS485 and RS232), Modbus ASCII
and Modbus TCP, which is the Modbus RTU protocol embedded into
TCP packets.
Modbus TCP is an internet protocol. The protocol embeds a Modbus
frame into a TCP frame so that a connection oriented approach is
obtained thereby making it reliable. The master query's the slave and the
slave responds with the reply. The protocol is open and hence highly
scalable.

5.2 Protocol Description

The Modbus protocol defines a simple protocol data unit
independent of the underlying communication layers. The mapping of
Modbus protocol on network can introduce some additional fields on the
application data unit.
WF-2000 Series Wi-Fi I/O User's Manual (Ver. 1.0, Sep./2012) ------------- 45