Technological Foundations

IO-Link communication takes place on a three- or four-wire unshielded standard cable that can establish an up to 20-meter-long connection between the IO-Link device and the IO-Link master. The IO-Link master is either located in the control cabinet or directly in the field. From there, it establishes the connection, or communication, between IO-Link devices and the automation system. A master can feature several IO-Link channels, known as ports, each of which can be used to connect one IO-Link device at a time. Devices can include a sensor, actuator, or RFID read/write device. This means IO-Link is not a bus system, but a point-to-point connection. In the so-called SIO mode, short for standard input and output, the sensor transfers its detection state as a 0 V and 24 V signal. Once IO-Link communication is activated at this master port, the master contacts the device and establishes the IO-Link communication. Master and device then communicate bidirectionally via the C/Q signal line using a coded sequence of signal states (coded switching).

An IO-Link master typically comes with several ports. Port configuration is used to determine the settings for each port. This is usually performed with a port configuration tool for a specific type of master or with an engineering tool for a specific control system. Settings for the following functions are available:

• Port mode (IO-Link, digital input, digital output, deactivated)
• Cycle time (“Free running” (as fast as possible), fixed cycle time)
• Expected device (manufacturer and device ID)
• Validation (no validation, check of the connected device with expected device)
• Data storage (deactivated, “restore-only,” backup and restore)

During operation, data on the current status of every port can be retrieved. In addition to the current communication status and IDs of the connected devices, this also includes information on the validity of the transferred process data and all diagnostic events.