IO-Link - Basics

IO-Link represents a communication system for the connection of intelligent sensors and actuators to an automation system in the IEC 61131-9 standard under the designation "Single-drop digital communication interface for small sensors and actuators" (SDCI).

Both the electrical connection data and the communication protocol are standardized and summarized in the IO-Link Spec.

IO-Link specification The development of the EL6224 was subject to the IO-Link specification 1.1. At the time of the preparation of this documentation, the IO-Link specification is entering the IEC standardization and will be adopted in extended form as IEC 61131-9. The new designation SDCI will be introduced at the same time. As a member of the respective committee, Beckhoff supports the development of IO-Link and reflects changes to the specification in its products.

An IO-Link system consists of an IO-Link master and one or more IO-Link devices, i.e. sensors or actuators. The IO-Link master provides the interface to the higher-level controller and controls communication with the connected IO-Link devices. The Beckhoff EL6224 IO-Link Master Terminal has four IO-Link ports. One IO-Link device can be connected to each of them. Therefore, IO-Link is not a fieldbus, but a peer-to-peer connection (see Fig. Peer-to-peer communication IO-Link).

The connected IO-Link devices have individual parameter information in the form of an IO device description (IODD), which is set with the KS2000 configuration software (see chapter KS2000 - Settings).

Parameter data exchange

An intelligent IO-Link device can support parameterization through SPDUs (service protocol data units). The PLC must explicitly query or, when marked as such, send these acyclic service data.

SPDU access TwinCAT currently only supports access via ADS.

The so-called SPDU index is used to address the corresponding parameter. The following ranges are available.

The use and implementation of these ranges is the responsibility of the sensor/actuator manufacturer.

For clarification, just a few of the possible indices are listed here; refer to the documentation for the IO-Link device used.