Operating Principle

IO-Link has specified three transfer rates, COM1, COM2, and COM3, which range from 4.8 and 38.4 up to 230.4 kbit/s. This means different transfer rates are available that correspond with the data volume of each device. Currently, most IO-Link devices can be operated with a transfer rate of 38.4 kbit/s (COM2).

To establish communication, the master first sends a wake-up event to the IO-Link device. The device recognizes the signal and waits for an initial message. The master then sends a fixed “start-up” message at the three transfer rates and the device responds with the transfer rate it supports. This establishes the lowest level of communication.

In the next step, the master reads additional communication parameters from the device followed by the manufacturer ID and device ID. This means that all information needed to set the required message format for the next steps is available in the master. As part of validation, the manufacturer ID and device ID for the respective port can be checked along with the connection status of the expected device.

The devices offer a wide range of functions with associated setting options and status information because of their communication capability. The IODD—short for IO device description— format was defined as a standard description language to simplify operation and display data and information in a user-friendly format. This description features the following information:

• Communication properties
• Supported product versions
• Parameter structure and value ranges
• Structure and content of process data
• Possible events
• Definition of user interface and menu structure
• Multilingual support for all parameters

Each IO-Link device has its own IODD that can be interpreted and displayed on all IO-Link-enabled system environments. This way, all IO-Link devices can be operated independently of the system.

To keep the integration of IO-Link devices as easy as possible for end users, the control system must have standardized program access to the devices.
This problem was solved by the implementation of IO-Link device profiles. These determine where a certain parameter/process value is to be located within an IO-Link-capable device. Data structure, data content, and the basic functionalities are specified in the device profiles. This means different data images and spending time familiarizing yourself with different parameter structures are a thing of the past.

“Smart Sensor Profiles” are the device profiles currently defined for IO-Link. Due to their prevalence, the latest expansion of the sensor profiles includes the following manufacturer-independent classifications of sensors:

• Fixed switching sensors (FSS)
• Adjustable switching sensors (AdSS)
• Digital measuring sensors (DMS)

Smart Sensor Profiles make available manufacturer-independent identification, parameterization, and diagnostics of IO-Link devices. Even control system integration, teach-in, and device replacement are associated with considerably less effort—with no limits on flexibility.