Modbus RTU to TCP converter
Slaves on an RS-485 line and a master that speaks only Modbus TCP. The Gateway puts a socket in front of the serial bus: a request from the master goes down the line, the slave's reply comes back, every function code forwarded. It is the Modbus converter node, a service beside the flow rather than a step in it.
Typical use case
A SCADA on the office network needs meters that sit on a serial bus in a switch room, and a dedicated serial-to-Ethernet box is one more device to buy and manage. An edge computer already running the Gateway does the conversion, and can poll the same bus for its own reporting at the same time.
Configuration approach
The serial side
Port, baud, parity, data and stop bits, and RTU or ASCII framing, the same vocabulary as a polled device.
The socket side
Modbus TCP, or MBAP over UDP for the vendors that ship it, on a bind address and port, with a limit on simultaneous masters.
Unit IDs
A map renumbers slaves when the master expects different IDs; an ID that maps nowhere is answered with exception 0B, as a real gateway would.
Writes off by default
Write function codes are refused with exception 01 unless forwarding is switched on, and validation warns every time it is: any master that reaches the port could then change the devices.
Questions engineers ask
Can the gateway poll the bus too?
Yes. A source node on the same serial port and the converter share one link; the requests queue in order.
Which licence?
Protocol conversion needs a Professional licence. A trial licence is Professional.
Build a Modbus RTU to TCP converter gateway
Create a project, define the device and its tags in the Edge Logic Editor, and download a runtime to test at the plant.