IO-Link systems have a three-tiered environment with logic and configuration data split across the PLC, the IO-Link master, and the various smart field devices. Machine truth is no longer contained solely within the PLC-centric development environment such as TIA Portal.
Here, “machine truth” is defined as the information a technician requires to restore the equipment in the 3 AM fog of troubleshooting. Detailed documentation and careful preservation of the golden files are essential for preventive and speedy corrective maintenance.
This article explores this tiered complexity by analyzing a representative mix of smart sensors and an IO-Link master that operates as a preprocessing node placed between sensors and the PLC. For clarity, the critical IO-Link to PLC interface is omitted. This article provides a high-level introduction to the PLC side of IO-Link with an emphasis on the role of the GSDML and IODD files.
Key Takeaways
- The IO-Link master itself may be configured as a small PLC with gate-level and timer-based logic.
- The IO-Link master will support both traditional and IO-Link enabled devices.
- A full PLC-based IO-Link integration is challenging. We are tempted to move programming and configuration to the sensors and IO-Link master.
- The decentralized setup increases the demands on technicians who must be proficient in multiple software environments.
- Documentation demands increase as the truth is distributed across devices.
This article is part of the DigiKey Field Guide for Industrial Automation
Location: Program It → Networks & Protocols
Difficulty: 
System Integrator — difficulty levels explained
Author: Aaron Dahlen | MSEE | Senior Applications Engineer, DigiKey
Last update: 02 Apr 2026
Distributed Intelligence Road Map
Control and configuration may be spread across three levels:
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PLC: The PLC is the primary machine controller. It handles overall combinational logic and sequencing for state-based control.
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IO-Link Master: The IO-Link master shown in Figure 1 (right) provides a “field logic layer.” This integration gateway includes limited PLC-independent logic for local device-to-device interactions. For example, a light stack could be controlled directly by a proximity switch with zero interaction with the PLC.
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Field Devices: In this context, field devices are the smart sensors, actuators, and display devices integrated into the system. These devices incorporate varying levels of intelligence, ranging from traditional teach-mode analog settings to complex programmable behaviors for alarms or state-based operation.
Language Clarification
We are tempted to use the term “edge processor” to describe the operation of the IO-Link master. This is a classification error when we consider the larger OT vs IT discussion. In this case, the IO-Link master does not interface with the IT side of industrial automation. It is exclusively in the machine-control (OT) domain of the PLC.
Instead, think of the IO-Link master as a field logic controller or a preprocessing node for the PLC. While the featured IO-Link master is not a safety device, it operates squarely in the PLC’s deterministic control domain.
Note that SICK uses the term Sensor Integration Gateway (SIG) to describe the operation of the IO-Link master. This is a good term to use, as it prevents misunderstanding the scope of the IO-Link network.
Architecture of a Distributed IO-Link Control System
The equipment shown in Figure 1 is used to demonstrate the distributed nature of the programming. These devices were chosen as each stores critical settings in a different location. None fall into the usual orderly IO-Link categories, yet each physically connects to the IO-Link master.
- SICK SIG300-0A04AA100 IO-Link Master (PROFINET Variant)
- SICK MPB10-VS00VSIQ00 Multi Physics Box for vibration and shock detection.
- Banner K50RPB-4030-LDQ radar sensor
- SICK UM18-217161101 ultrasonic distance sensor
- Banner K100PDBLRGBD15AQ text display (rotating) with integral multicolor beacon
Figure 1: Collection of smart sensors and an IO-Link master.
SICK SIG300 IO-Link Master
The SICK SIG300 has a PLC-like programming environment.
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Port configuration: The first step is to configure each M12 port. This starts with permissions where each port is configured for either PLC or local control. The individual ports may then be configured as IO-Link, digital input, or digital output.
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Control Logic: Assuming the SIG300 is in local control, the logic editor may be used to configure port-to-port connections with PLC-like logic and timing control. An example is included in Figure 2 showing the drive logic associated with the Banner K100 beacon. The OR gates drives port S6 pins 4, 2, and 5.
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PLC Cyclic: With this mode, the PLC reads and writes to field devices connected to the IO-Link master. From the PLC perspective, this is a background process similar to reading and writing to the PLC’s local I/O.
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PLC Acyclic: This is the most complex operating mode as the PLC will interact directly with the IO-Link master. An example is passing configuration data to a full-featured IO-Link sensor.
The distinctions are not mutually exclusive as truth may be spread across all configuration and control layers.
In my opinion, the most maintainable solution is full PLC control via the cyclic and acyclic interface. This places a single source of machine truth within the PLC. Unfortunately, it is a costly programming effort. Also, some devices do not directly support this mode. Finally, the very fact that the SIG300 includes a logic editor suggests the PLC-based solution is not always the best answer.
Figure 2: Logic editor programming window showing the drive connection to the Banner K100 beacon.
SICK MPB10 Multi Physics Box
The SICK Multi Physics Box is designed to measure vibration, shock, and temperature. It is a true IO-Link device that may communicate directly with the PLC (via the IO-Link master). It may also be configured to provide a discrete digital output for a chosen vibration or shock when a user-configured threshold is exceeded.
In this example, it has been programmed to respond to any shock event greater than 10 g. For this application, we are using the sensor’s discrete digital output on M12 connector pin 2.
The sensor is configured using the SICK SOPAS Engineering tool and the SICK SILink2 Master (sold seperately). Example configuration and data are included in Figure 3. The graph shows the sensor’s response to a sharp knuckle rap to the sensor.
The sensor settings include:
- Shock threshold values
- Device configuration to use shock instead of vibration
- I/O setup for the discrete as well as analog output pins.
Figure 3: Programming window for the SICK Multi Physics Box.
Banner K100 Display
The K100 is a text display with integrated multicolor status indicator LEDs. It is programmed using the PRO-KIT programmer (sold separately). The programming technique is identical to the Banner SD50 display and the K50 multicolor touch button. These devices are programmed via the computer’s USB port using Banner Pro Editor software.
For this application, a preprogrammed display message is selected via a binary signal applied to the display’s three control wires. This configuration is encoded into the Banner software as shown in Figure 4.
| Binary Code | Text to be Displayed |
|---|---|
000 |
DigiKey |
001 |
Radar Trig |
010 |
Physics Trig |
011 |
Sonic Trig |
100 |
Color Trig |
101 |
Sonic Teach |
110 |
Color Teach |
Notes:
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The SIG300 to Banner K100 M12 interface has three available control wires (black, white, and gray). The number of unique messages is therefore limited to eight. To access all 16 messages we would need to also control the power (brown) wire. This could be done with a flying lead cable. However, the convenience of the M12 connector is lost.
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The featured Banner display is hard-coded using the Banner Pro Editor software. It cannot be changed on the fly. We could move to full IO-Link PLC control by selecting the related Banner K100PDBLRGBKAQ beacon.
Figure 4: Programming window for the Banner display.
Banner K50 Radar
The Banner K50 radar is described in this supporting article.
The featured radar is not IO-Link capable. Consequently, there are additional settings that the technician must configure including:
- Object detection threshold. This includes min and max response zones as well as settings for “sense strongest peak” or “sense closest peak.”
- Configuration of the discrete outputs.
- Control of the LED indication display.
Note that a newly released IO-Link enabled K50RB-4030-LKDQ is available.
SICK UM18 Ultrasonic Sensor
The SICK UM18 is a conventional ultrasonic sensor that can be taught to trigger at a distance between 20 and 150 mm. The teaching is similar to other sensors where the object is placed into the sensor’s field of view. A control line is then asserted to latch the switching threshold into the sensor’s memory.
What is the greatest challenge with distributed IO-Link control?
This article presents four unique sensors that physically connect to the IO-Link master’s M12 ports. Together, they present a system integration challenge as the programming and configuration data are spread across multiple devices.
We are left with an important decision.
Do we accept distributed machine truth or do we insist on full integration of IO-Link functionality, thereby moving truth to the PLC with cyclic and acyclic communication?
There are good arguments for each approach. Whatever you decide, document everything:
- What devices need to be programmed?
- Where are they located?
- What software is required to program each device?
- What needs to be configured?
- What are the exact configuration settings?
- What institutional controls protect the golden file for the IO-Link master’s logic editor program?
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About This Author
Aaron Dahlen, LCDR USCG (Ret.), is a Senior Applications Engineer at DigiKey in Thief River Falls. His background in electronics and industrial automation was shaped by a 27-year military career as both technician and engineer, followed by over a decade of teaching.
Dahlen holds an MSEE from Minnesota State University, Mankato. He has taught in an ABET-accredited electrical engineering program, served as coordinator of an electronic engineering technology program, and instructed military technicians in component-level repair.
Today, he has returned to his home in northern Minnesota, completing a decades-long journey that began with a search for capacitors. Read his story here.