Modbus: The Universal Industrial Protocol (RTU and TCP)
Modbus is the most widely used industrial protocol in the world. Created in 1979 by Modicon, it is used in millions of PLCs, inverters, drives, meters, and sensors. Its simplicity is its strength: a master communicates with slaves via registers (coils, inputs, holding registers), without session negotiation.
- Modbus RTU — RS-485 or RS-232 serial connection, up to 247 slaves per bus, compact frames with CRC.
- Modbus TCP — encapsulated in TCP/IP over Ethernet, IP addressing, no limit on the number of slaves per segment.
Virtually all industrial equipment uses Modbus. It is the essential starting point for any IoT integration.
Detailed Resources:
OPC UA: The Open Standard for Industry 4.0
OPC UA (Unified Architecture) is the standard protocol for Industry 4.0 interoperability. Unlike Modbus, it incorporates object-oriented modeling, native security (authentication, TLS encryption), and a service discovery mechanism.
OPC UA runs on TCP/IP (port 4840) or WebSockets. It is mandated by numerous standards (Industry 4.0, RAMI 4.0) and adopted by major PLC manufacturers (Siemens, Beckhoff, B&R, etc.).
Its main use in the IoT context is to expose data from a PLC or SCADA server to a gateway, which then pushes the data to the cloud via MQTT.
Resource: OPC UA to MQTT
RS-485: The Industrial Serial Interface
RS-485 is an electrical standard (not a protocol) that defines a multipoint differential bus. Most industrial serial protocols (Modbus RTU, M-Bus, BACnet MS/TP) use RS-485 as their physical layer.
Key Features:
- Distance: up to 1,200 m at 100 kbps
- Electromagnetic interference resistance (shielded twisted-pair cable)
- Up to 32 standard drivers/receivers (256 with high-impedance transceivers)
- Two-wire power supply for M-Bus meters (2-wire variant)
To connect an existing RS-485 bus to the cloud without changing the wiring, an industrial Ethernet-to-serial gateway or a 4G gateway is connected directly to the bus.
Resources:
MQTT: The Cloud-Based IoT Protocol
MQTT (Message Queuing Telemetry Transport) is the leading IoT protocol for sending data to the cloud. Its publish/subscribe model, which uses a central broker (Mosquitto, HiveMQ, AWS IoT, etc.), decouples data producers from consumers.
Benefits for industrial IoT:
- Very low overhead (minimum 2-byte header) — ideal for cellular networks
- Native support for disconnection and reconnection (QoS 0, 1, 2)
- “Last will” message to detect link loss
- TLS for end-to-end encryption
The IoT gateway translates Modbus messages into structured MQTT topics (JSON or binary) and publishes them to the cloud broker.
BACnet and M-Bus: Building Automation and Remote Meter Reading
BACnet (Building Automation and Control Network) is the open standard for building automation. It defines semantic objects (temperature, light level, setpoint, alarm) and operates over BACnet/IP (Ethernet) or BACnet MS/TP (RS-485). It is used in HVAC, lighting, access control, and fire protection systems.
M-Bus (Meter Bus) is the European standard (EN 1434, EN 13757) for remote meter reading: cold water, hot water, gas, heat, and electricity. The wired (2-wire) version powers the meters from the concentrator. The Wireless M-Bus (868 MHz) version eliminates the need for wiring.
Resources:
Comparison Table of Industrial Protocols
| Protocol | Medium | Typical Speed | Main Use Case | Guide |
|---|---|---|---|---|
| Modbus RTU | RS-485 / RS-232 | 9,600–115,200 bps | PLCs, sensors, meters | → |
| Modbus TCP | Ethernet TCP/IP | 10–1,000 Mbps | PLCs on IP networks | → |
| OPC UA | Ethernet TCP/IP | 1–1,000 Mbps | Industry 4.0, business information systems | → |
| RS-485 | Twisted-pair | 100 kbps–10 Mbps | Multi-device fieldbus | → |
| MQTT | TCP/IP (cloud) | Network-dependent | IoT data upload to the cloud | → |
| BACnet/IP | Ethernet | 10–100 Mbps | Building Management System (BMS), HVAC, building | → |
| BACnet MS/TP | RS-485 | 9,600–76,800 bps | Building Management System (BMS) field | → |
| M-Bus | Twisted pair | 300–9,600 bps | Remote meter reading | → |
| Wireless M-Bus | 868 MHz radio | Low data rate | Wireless meter reading | → |
Our Solutions by Protocol
Each protocol has its own integration page with detailed architecture diagrams and use cases:
| Solution | Description |
|---|---|
| Modbus RTU to Cloud | Uploading Modbus RTU/RS-485 data to a cloud platform |
| Modbus TCP to Cloud | Modbus TCP over Ethernet to cloud monitoring |
| Modbus RTU to MQTT | Conversion of Modbus RTU to MQTT topics |
| Modbus Meters | Integration of Modbus register-based meters |
| OPC UA to MQTT | OPC UA → MQTT bridge for Industry 4.0 |
| RS-485 Modbus 4G | RS-485 bus connection via 4G/LTE modem |
| Industrial Ethernet Serial Gateway | RS-485/232 to Ethernet conversion on DIN rail |
| BACnet to Cloud | BACnet Building Management System integration into the cloud |
| M-Bus to Cloud | M-Bus concentrator with cloud data upload |
| Wireless M-Bus Remote Reading | 868 MHz wireless remote reading without wiring |
| Industrial Data Upload | Complete multi-protocol data upload architecture |