Technology

Modbus TCP and RTU integration: register maps and byte order

We read Modbus devices, from energy meters to drives and temperature controllers, and turn their registers into a meaningful data model.

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Our clients

Siemens
Anadolu Isuzu
BSH
Tofaş
Toyotetsu
Martur
Turkcell
Vodafone
Doğadan
Pakmaya
Bross
Abdi İbrahim
Nobel İlaç
Plastimak
Dalgıç Kalıp
Barbaros Motor
Magneti Marelli
Rözmaş
Sanel

Modbus is one of the most common field protocols: devices hold data in numbered registers and serve them request by request. Modbus TCP runs over Ethernet on port 502; Modbus RTU runs on serial lines such as RS-485.

In plants, Modbus usually means energy meters, variable frequency drives, temperature and humidity controllers, and compressor or chiller controllers. Data arrives by address, not by name: which register holds which value, with what scale and byte order, comes from the register map in the device documentation.

VOLSOFT turns those maps into per-model device profiles, sets up the reading on Proxus and delivers values with units to energy monitoring, process monitoring and OEE screens. We do not sell devices; the serial device server needed for RTU lines is standard hardware of the plant's choice.

What we deliver

Modbus integration

Modbus TCP

Ethernet devices are read on port 502. Datasheet addresses such as 40001 are entered as they are and converted automatically.
Modbus RTU and ASCII

Serial devices are read with RTU over TCP or ASCII over TCP through a serial device server that carries the RS-485 line over TCP. Proxus does not open serial ports directly.
Register maps and functions

Holding and input registers, coils and discrete inputs are defined separately. Each point's address, type, scale and unit go into the profile.
Byte and word order

32-bit integers and floats span two registers, and word order varies by vendor. We confirm it from the documentation and by comparing with live values.
Unit IDs and line load

Several devices on one line are told apart by unit ID. We tune read intervals and request grouping to what the serial line can carry.

How a project runs

From discovery to live, step by step

01
Device list

We record make and model, TCP or RTU connection, IP or serial line details and unit IDs for every Modbus device.
02
Register maps

For each model we pick the needed values from the register map and build a device profile with type, scale and byte order.
03
Read and verify

We start reading on a Proxus edge gateway and compare values with the device display or a reference measurement.
04
Model and reports

Values go into the shared data model and on to energy, process and OEE screens.

Built on Proxus

Proxus's Modbus driver covers Modbus TCP, RTU over TCP and ASCII over TCP and runs on the edge gateway. A device profile built for one model applies to every device of that model, and values can go on to MQTT, databases or the cloud.

Proxus is the industrial data platform built by the VOLSOFT team.

Proxus Modbus driver ↗

Frequently asked questions

Common questions

What is Modbus TCP?

Modbus TCP is Modbus over Ethernet using TCP/IP, on port 502 by default. Device data sits in numbered registers that the client reads by address.

What is the difference between Modbus TCP and Modbus RTU?

Modbus TCP runs over Ethernet and Modbus RTU over serial lines such as RS-485; the register model and function codes are the same. With a serial device server, RTU devices can be read from the same system as Modbus TCP devices.

Why do Modbus values look wrong?

Usually because the word or byte order of 32-bit values is set wrong, or addresses are off by one. A missing scale factor is another common cause. We verify every profile against the device's own display.

Can energy meters be read over Modbus?

Yes, most industrial energy meters offer Modbus TCP or Modbus RTU. Current, voltage, power and energy counters are read from the register map and fed into energy monitoring.