7 Modbus/TCP – SmartWire-DT implementation
6.2 Manufacturer-specific object classes
72 SmartWire-DT Gateway EU5C-SWD-EIP-MODTCP 08/17 MN120003Z EN www.eaton.com
7 Modbus/TCP – SmartWire-DT implementation
The Modbus-TCP communication system is based on the TCP/IP protocol
being used. All data and parameters are entered into the TCP/IP frame's use-
ful information data range. This data is integrated into a special MBAP frame
that ensures that the data will be interpreted unambiguously. "MBAP" stands
for ModBus Application Protocol. Special function codes are used to access
the data (function codes 1 - 255).
Communications between Modbus modules are based on the client/server
principle. The client, e.g., the PLC, uses function codes to transmit a request
to the server, e.g., the EU5C-SWD-EIP-MODTCP gateway. The server
responds to the request and returns the requested data to the client. If an
error occurs during the communication request, e.g., because a request is
not permitted, the client will receive an error message.
Data model and Modbus registers
In principle, Modbus differentiates between bit data and word data. Each of
these is further subdivided into two available types:
These data structures are provided from the Modbus server side. The scope
of the data access functions and the maximum number of data objects are
both independent of the specific implementation being used.
In the case of Modbus, there are multiple addressing methods that can be
used to access the data in the PLC. Their use depends on the selected PLC
and the corresponding programming system. For example, when using the
5-digit addressing method, the PLC will work with an offset of 40001 and the
entire data storage area will be offset by this number.
All references in this documentation are specified as hexadecimal values.
Data Object Data type Access maximum number
Input Status BIT Read 65536
Coil Status BIT Read / Write 65536
Input Register Word Read 65536
Holding register Word Read / Write 65536
￫
The EU5C-SWD-EIP-MODTCP gateway only supports access to
input and output registers.
To Next Page
Loading...
