Connect Devices via Modbus
About Modbus
The Modbus protocol is a widely used communication protocol that was developed in 1979 by Gould-Modicon. It is based on a client-server architecture, in which a master device (usually a computer) is connected to one or more slave devices. This protocol makes it possible to monitor and control various measuring devices from a central system. Data transfer can take place via one of three variants: ASCII, RTU, or TCP.
In Eliona, Modbus TCP and RTU over TCP are mainly used; however, the platform also offers support for other schemes such as UDP and RTU over UDP to enable the flexible integration of older or special devices.
Modbus TCP
With Modbus TCP, data is transferred via Ethernet in binary form using TCP/IP packets. The standard port 502 is reserved for this purpose. For older devices with serial interfaces, a protocol converter or router can be used to integrate them into the TCP system.
Roles in the Modbus Protocol
Modbus Client (Master)
Communicates with a remote device.
Sends Modbus requests that are controlled by the application.
Transmits these requests to the Modbus client interface.
The client is usually the device that retrieves the data (e.g., a PC or Modbus Poll).
Modbus Server (Slave)
Waits for Modbus requests (via TCP port 502).
Reads and processes these requests.
Returns Modbus response messages.
The server is usually the device that provides the data (e.g., a PLC or a sensor).
Procedure for Connecting Devices via Modbus
To connect devices to Eliona via Modbus, follow these steps:
Establish a connection to a Modbus server (slave)
To establish a connection to a Modbus server (slave), you need the IP address and the port of the server. The standard port for Modbus TCP is 502.
Read or write registers
After the connection has been successfully established, the Modbus client (master) can send requests to the Modbus server. These requests are used to read or write registers on the server.
Read: The client reads specific values from the server's register addresses.
Write: The client sends data and writes it to the server's registers. ⚠ Note: All requests are initiated by the client.
Internal Modbus Versions in Eliona
In Eliona, several Modbus protocols are supported to integrate different device types and networks:
Modbus TCP: Enables communication via Ethernet with the standard port 502.
RTU over TCP: Enables the integration of devices with the older RTU protocol via a TCP connection.
UDP: Provides a connectionless transmission option for Modbus messages.
RTU over UDP: Uses the RTU protocol over UDP to integrate devices with low connection overhead into the network.
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