Industrial Engineer · phase 15 of 16 · noun

Modbus RTU / Modbus TCP

The Explain card

Plain English: On a drive, Modbus is the register map through which a PLC or SCADA reads and writes parameters, commands and feedback. RTU rides a serial port, TCP rides the Ethernet port, and the register numbers are the same either way.
Example: A small drive with no option card exposes its run command in one holding register and its speed reference in the next. The PLC writes both and reads the status register back.
Why it matters: Modbus is the universal fallback for drive communication, on almost every brand, with no vendor tools needed. It is polled rather than cyclic, so it is fine for a pump and wrong for anything that needs a fast, guaranteed update.
Hook: The register map every drive speaks, slowly.

How the word is built, where it came from, and what it sits beside in memory.

In a sentence

During commissioning, the technician sets the VFD device address and verifies that Modbus RTU returns the motor-current register to the PLC.

Why these words

Modbus English trade coinage by Modicon, combining Modicon and bus names the protocol family
RTU initialism of remote terminal unit identifies the serial framing variant

Where it came from

Origin: English trade coinage introduced by Modicon, with RTU formed from remote terminal unit
Entered the language: 1979
What changed: Modbus began as a single protocol name, then gained qualifiers such as RTU and TCP as distinct communication forms were standardized.

How it is spelled

Spelled like

Broken into chunks

What it sits beside

Same subject

Same shape

Modbus variants

industrial network initialisms

Phase 15: VFD Parameters and Communications

The parameter set itself, and the network words a controller uses to read and write it while the machine is running.