A Raspberry Pi HAT called "IOL HAT" implements an IO-Link master on the single-board computer's 40-pin GPIO header, opening the Raspberry Pi platform to industrial sensors and actuators that speak IEC 61131-9. The product, surfaced by CNX Software, targets developers wiring IO-Link devices into IIoT edge nodes without buying a dedicated industrial master.

What the IOL HAT actually does

The module performs the master side of an IO-Link link. A master is the controller-side device that:

• Polls one IO-Link device per port on a fixed cycle
• Exchanges process, parameter, and diagnostic data
• Stores each device's IODD (IO Device Description) file
• Replaces the analog 4-20 mA loop or discrete I/O that preceded it

CNX Software frames the board as an entry point for industrial IoT prototyping, where users can run Python, Node-RED, or containerized PLC stacks directly on the Raspberry Pi.

Why IO-Link matters for instrumentation

IO-Link (IEC 61131-9) is a single-drop, point-to-point digital protocol sitting below the fieldbus level. Engineers specify it for one reason: it brings digital transparency to the last meter of cabling. A voltmeter, photoelectric sensor, or pneumatic valve block reports its part number, measured value, and fault state in machine-readable form rather than as an opaque current loop.

Key technical parameters of the standard:

• Up to 20 m of unshielded three- or four-wire cable per port
• Three communication speeds: COM1 at 4.8 kbit/s, COM2 at 38.4 kbit/s, COM3 at 230.4 kbit/s
• Cycle times from 0.4 ms (COM3) to 2.6 ms (COM1), suitable for closed-loop control
• Up to 32 bytes of process data per cycle in the standard frame
• Hot-swappable device replacement with automatic re-parameterization

Master hardware from Balluff, IFM, Turck, and Phoenix Contact typically ships in four- or eight-port configurations with IP67 ratings. A Raspberry Pi-based master inherits none of that industrial hardening unless the integrator adds it.

What the Raspberry Pi brings to the table

Pairing an IO-Link master with a Pi changes the cost calculus for small-scale deployments:

• Per-unit hardware cost in the tens of dollars, an order of magnitude below dedicated masters
• Native Ethernet, Wi-Fi, and (via USB or HAT add-ons) cellular for cloud backhaul
• Onboard compute for MQTT brokers, time-series databases, or OPC UA pub/sub bridging
• GPIO and USB for ancillary sensors not covered by the IO-Link spec

The trade-off is equally concrete: no IP-rated enclosure, no industrial temperature range by default, and no pre-certified EMC report.

What the buyer still needs to verify

The CNX Software report positions the IOL HAT as a development tool, not a turnkey industrial component. Before substituting it for a hardened master in a CE-marked machine, integrators must confirm:

• Operating temperature window versus the plant's worst-case ambient
• Conducted and radiated EMI performance under IEC 61000-6-2
• IEC 61131-9 conformance test results from the master vendor
• Functional-safety implications where the IO-Link device sits inside a safety loop

Until those questions are answered in writing, the IOL HAT belongs in the prototyping rack rather than on the production line. The open question for the industrial market is whether any third-party lab will publish a formal IEC 61131-9 conformance certificate for this class of Pi-hosted master.