Specifications

STB NIP 2311 Services
116
EIO0000000051 6/2010
Modbus TCP Device Implementation
The Modbus application layer is very simple and universally recognized. Thousands
of manufacturers are already implementing this protocol. Many have already
developed Modbus TCP/IP connections, and many products are currently available.
The simplicity of Modbus TCP/IP enables any small field device, such as an I/O
module, to communicate over Ethernet without a powerful microprocessor or a large
amount of internal memory.
Modbus TCP/IP
The same application protocol is used for Modbus serial link, Modbus Plus, and
Modbus TCP. This interface routes messages from one network to another without
changing the protocol. Because Modbus is implemented above the TCP/IP layer,
you can also benefit from the IP routing, which enables devices located anywhere
in the world to communicate regardless of the distance between them.
Schneider offers an entire range of gateways for interconnecting a Modbus TCP/IP
network to already existing Modbus Plus or Modbus serial link networks. For further
details, consult a Schneider Electric regional sales office. The IANA institute has
assigned to Schneider port TCP 502, which is reserved for the Modbus protocol.
Modbus Messaging Summary
The transfer of information between a Modbus client and server is initiated when the
client sends a request to the server to transfer information, to execute a command,
or to perform one of many other possible functions.
After the server receives the request, it executes the command or retrieves the
required data from its memory. The server then responds to the client by either
acknowledging that the command is complete or providing the requested data.
The system response time is limited by two main factors, the time required for the
client to send the request/receive the response and the ability of the server to
answer within a specific amount of time.
1 retrieved data
2 client request
3 server response
4 data retrieval