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Modbus FAQ for Automation Engineers

What Is Modbus?

Modbus TCP is a widely used communication protocol in industrial automation. It enables different devices, such as PLCs, sensors, drives, and precision tools like Kolver’s K-DUCER, to exchange data over Ethernet connections.

For automation engineers, Modbus is almost plug-and-play: most Ethernet-capable PLCs and industrial PCs/MES systems already support it.

Key Features of Modbus

  • Client/Server architecture
  • Lightweight and easy to implement
  • Pre-implemented in virtually all ethernet-capable PLCs
  • Open standard with no licensing fees




Why is Modbus important in the manufacturing world and in precision fastening?

Modbus is important in manufacturing because it provides a simple, reliable, and widely adopted way for machines to talk to each other, and it's also a foundational enabler of Industry 4.0 (even if it might not be not the most modern or advanced protocol). It’s a sort of universal “lingua franca” in automation, whether you have a 20-year-old PLC or a new smart electric screwdriver like Kolver’s K-DUCER. Its easy implementation and troubleshooting have kept it relevant for almost 50 years.

For companies modernizing their factories, Modbus is often the easiest starting point for creating connected production lines.




How does Modbus work?

A Modbus client (e.g., PLC, SCADA, or MES) sends requests to a Modbus server (e.g., a K-DUCER controller) to either:

  • Read registers (e.g. torque, angles, graphs)
  • Write registers (e.g. change parameters or switch programs)

The server responds with either the requested data or an acknowledgment.




Which Kolver Products Support Modbus?

All of Kolver’s premium tools offer Modbus TCP as standard, no license required:

  • K-DUCER series (KDU-1A)
  • K-DUCER MicroTorque (KDU-NT)
  • K-TESTER Torque Testers




How do I set up Modbus TCP on the K-DUCER?


Step 1: Configure the K-DUCER

  • Navigate to: General Settings → Page 4 on the KDU touchscreen.
  • Select protocol: Modbus TCP or a combo (e.g., OP + MB)
  • Set IP address (e.g., 192.168.1.100)
  • Set subnet mask (e.g., 255.255.255.0)
  • Ensure no IP address conflicts with other devices

Step 2: Connect from PLC or PC

  • Use Modbus TCP client library or PLC Modbus function block
  • Open TCP socket to port 502 on the KDU's IP
  • If using a Siemens S7 series PLC, use Kolver's pre-built function blocks

Step 3: Send Commands

Specify in each command:

  • Function code (e.g., 0x03)
  • Register address (from Kolver’s Modbus map)
  • Value to write or variable to store response



What Is a Modbus Map?

A Modbus map is a device-specific table that defines the location and structure of data within a Modbus server device. The automation engineer will need to refer to the map when setting up the Modbus TCP communication between their PLC (or other client device) and the KDU controller.

The Modbus map specifies:

  • What the data represents: Temperature readings, torque values, status flags, etc.
  • Where the data is located: Specific register addresses within the device’s memory
  • How the data is formatted: Data types (integer, floating-point, boolean) and word order (endianness)

For the K-DUCER line, a link to the Modbus map is provided in the product page (Modbus Map and Manual link). The archive also provides code examples showcasing how to communicate with a K-DUCER controller via Modbus TCP on various platforms.

Please note that the KDU-1A and KDU-NT use slightly different Modbus maps. Make sure you refer to the correct one for your torque controller!



What is an example of a Modbus command in Python?

from pyModbusTCP.client import ModbusClient #pip install pymodbustcp
kdu_ip_address = '192.168.5.16'

my_client = ModbusClient(host=kdu_ip_address)
print(f'Torque (cNm) and angle (degrees): {my_client.read_input_registers(322,2)}')

This example prints the torque and angle result from the last tightening on a K-DUCER controller.




What are common Modbus function codes?

0x03         Read Holding Registers        Read read-write data

0x04         Read Input Registers           Read read-only data 

0x06         Write Single Register           Update one setting or value 

0x10         Write Multiple Registers       Bulk update settings or parameters





What is the difference between Modbus TCP and OpenProtocol?

Modbus and Open Protocol are two different communication protocols used in industrial automation. Both are supported by Kolver’s K-DUCER and K-TESTER lines.

Open Protocol was designed specifically for fastening data traceability and process control of smart torque screwdrivers and nutrunners.

The main advantage of Open Protocol for fastening is that it provides a standardized, structured way to communicate with smart torque tools, enabling seamless integration with MES and SCADA systems. Unlike general purpose protocols like Modbus, Open Protocol is specifically designed for tightening applications—it supports commands like job selection, VIN input, and detailed result reporting (torque, angle, OK/NOK, timestamp, prevailing torque, running torque, and more). Because of this, if your MES or SCADA system already supports Open Protocol (also known as Torque Tool Open Protocol), then it will work with the K-DUCER controller with minimal configuration. On the other hand, if your MES, SCADA, or PLC system does not support Open Protocol, it will be faster to integrate the K-DUCER using Modbus TCP.

TLDR; If your MES or SCADA supports Open Protocol, use it.
Otherwise, Modbus TCP is faster and easier to integrate for custom or legacy systems.



Why Am I Getting a “Modbus Server Busy” Error?

This typically occurs if:

  • The screwdriver motor is running while you're sending a write command
  • A user is interacting with the KDU touchscreen menus at the same time

Try queuing your write requests after the tightening cycle ends.



Can I modify K-DUCER programs via Modbus?

Yes, but it’s best to pre-configure programs via:

  • The KDU touchscreen
  • K-EXPAND software (free)
  • Or via a USB backup/restore

Use Modbus TCP mainly for:

  • Program selection
  • Real-time control
  • Torque/angle data acquisition

This keeps your PLC logic simpler and more robust.



Are torque and angle graphs available via Modbus?

Yes. You can retrieve real-time torque and angle curves and display them on your PLC, MES, or PC system.




Why does Modbus still matter after 50 years?

Modbus continues to be popular because it’s:

  • Simple and robust
  • Vendor-neutral and supported by most PLCs and HMIs
  • A common entry point for Industry 4.0 adoption
  • Ideal for legacy-modern integration (connects 20-year-old PLCs to smart screwdrivers)

In precision fastening, Modbus enables:

  • Real-time torque and angle monitoring
  • Traceability for quality control
  • Programmatic control of fastening operations



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Do you need more information?