PROJECT — COMMISSIONING DAY

Wire up a real plant — six devices, six protocols, one PLC.

Estimated 12 minutes.

It's your first day on the plant floor.

Seven devices are sitting in front of you, all unplugged: an operator HMI, the central PLC, a 6-axis robot, a servo drive, a smart sensor, a VFD motor drive, and a cloud gateway. Each one only speaks one protocol. Your job is to wire each device to the PLC using the right cable.

Why is the floor heterogeneous?

Real plants mix IT, OT, and motion. Each layer chose its protocol decades ago based on what it had to do — and those choices are sticky. Motion engineers picked EtherCAT because it cycles in microseconds. IT picked OPC UA because it speaks JSON-like schemas over TCP. Sensor vendors picked IO-Link because it shares the same 3-wire cable they already had. No single protocol wins the whole plant.

The crib sheet — what fits where.

HMI ↔ PLC = OPC UA · Robot ↔ PLC = EtherNet/IP · Servo ↔ PLC = EtherCAT · Smart sensor ↔ PLC = IO-Link · VFD ↔ PLC = Modbus RTU · Cloud ↔ PLC = MQTT/Sparkplug. Two distractor cables (Profinet, Profibus) sit in the palette — picking them on the wrong device gets you a labeled rejection from that device, not a streak reset.

Wire the plant.

Pick a cable in the palette, then click the connection line between the PLC and a device. Right cable: the cable lights up, the device comes alive. Wrong cable: the device tells you which protocol it actually expects, and you keep trying. All six right = production line lives.

You commissioned a real plant.

  • OPC UA bridges IT and OT — vendor-neutral, structured, secure. It's the modern HMI ↔ PLC link.
  • EtherCAT runs coordinated motion in sub-millisecond cycles. Servos don't take Modbus RTU.
  • IO-Link uses the same 3-wire cable as a normal sensor, but every smart sensor exposes parameters and diagnostics on top.
  • Modbus RTU still wins on cheap devices (VFDs, meters, controllers) because it's simple and free.
  • MQTT/Sparkplug B is how OT data leaves the plant — pub/sub, lightweight, broker-friendly.
  • EtherNet/IP is the Rockwell-side counterpart to Profinet — same role, different ecosystem.

Plant on line.

  • One PLC. Six languages. One running factory.
  • When you face a real plant, look at the device's nameplate / data sheet — it will tell you what protocol it speaks. The PLC almost always supports the rest.
  • You've seen the full protocols section. From here, dive into the specific protocols you'll actually use.