Modbus TCP / RTU integration

Since its inception in 1979 Modbus has become a widely used communication protocol in the field of industrial automation. Originally based on serial interfaces (RS232 and RS485) Modbus RTU enjoys widespread use throughout many different industries. Since then Ethernet has become the network of choice and many industrial devices now have native Ethernet interfaces. Modbus TCP is used over Ethernet and most SCADA networks have adopted this as their protocol of choice but there are challenges when it comes to connecting Modbus TCP and Modbus RTU networks together.

This document identifies common scenarios and looks at each can be overcome.

Modbus TCP to Modbus RTU

In this scenario a Modbus gateway is required. In communication terms a gateway is a device that can translate between 2 different protocols, in this instance Modbus TCP and Modbus RTU.

MODbus tunnelling
Modbus TCP to RTU via a Modbus Gateway

The gateway receives Modbus TCP requests on its Ethernet interface, converts and sends them out of its serial interface as Modbus RTU with the reverse being true when the data travels in the opposing direction.

Tunnelling Modbus RTU over Ethernet

This solution allows serial based Modus RTU devices to communicate over an Ethernet or IP network. A Modbus TCP tunnel is established between the 2 Modbus gateways and Modbus RTU commands are translated and transported through this tunnel in a completely transparent manner.

Tunnelling Modbus RTU over Ethernet / IP
Tunnelling Modbus RTU over Ethernet / IP

Distance limitations associated with Modbus RTU and RS485 can easily be overcome by utilising Ethernet.

Modbus RTU software on host with no serial interface.

Modbus RTU applications that reside within hosts that have no serial interfaces can easily be connected to Modbus RTU devices by the use of a serial server.

Virtual Realcom port
Modbus RTU connectivity via Virtual COM

Our serial servers enable you to create a virtual COM port. A virtual COM driver will need to be installed on the host where the Modbus application resides. Once installed this virtual COM will allow the Modbus RTU software to talk natively to the Modbus RTU devices through the serial server.