ModbusLite for Arduino Opta
ModbusLite_Arduino is a lightweight, industrial-grade Modbus SDK built specifically for the Arduino Opta platform. It brings the reliability and structure of our Linux-based Modbus SDK into the embedded Opta environment — with support for both Modbus TCP and Modbus RTU communication.
🧠 Overview
ModbusLite_Arduino provides a consistent and portable API that allows the Opta to operate as:
- 🖧 Modbus TCP Master or Slave over Ethernet
- 🔌 Modbus RTU Master or Slave over RS485
- ⚙️ A future-ready hybrid bridge between TCP ↔ RTU networks
It was developed to ensure stable, crash-free operation on industrial Opta PLCs while maintaining full interoperability with the existing Linux ModbusLite SDK.
🏭 Industrial Motivation
In industrial automation, you often have a mix of devices:
- Field sensors and actuators speaking Modbus RTU (RS485)
- Gateways and controllers using Modbus TCP (Ethernet)
- Edge devices like Raspberry Pi or Linux-based controllers running custom logic
The Opta sits perfectly in between — acting as:
- A Modbus master collecting data from remote devices
- A slave exposing local process variables
- Or a bridge, forwarding Modbus data between fieldbus and network domains
However, standard Arduino Modbus libraries are too heavy, unstable, or inflexible for real industrial use. ModbusLite_Arduino was designed to solve that.
🚀 Key Features
- Full Modbus/TCP and Modbus/RTU compliance
- Optimized for Opta’s mbed OS stack — no crashes or watchdog resets
- Unified ModbusLite API shared with the Linux SDK
- Lightweight memory footprint suitable for real-time control
- Asynchronous-ready architecture for future expansions
- Cross-platform interoperability with Linux and other controllers
🔧 Supported Modes
| Mode | Description | Typical Use Case |
|---|---|---|
| Modbus TCP Master | Opta polls Modbus TCP slaves over Ethernet | Control or data aggregation |
| Modbus TCP Slave | Opta exposes holding/input registers to TCP masters | PLC data access |
| Modbus RTU Master | Opta sends Modbus frames over RS485 | Fieldbus device control |
| Modbus RTU Slave | Opta responds to serial Modbus queries | Local register interface |
🔩 Example Scenarios
1️⃣ Opta TCP Master ↔ Opta TCP Slave
Two Optas exchange register data over Ethernet. Used to simulate control between nodes or test register mapping.
2️⃣ Opta TCP Master ↔ Linux Modbus SDK Slave
Demonstrates interoperability with industrial gateways or simulators.
3️⃣ Opta RTU Master ↔ Opta RTU Slave
RS485-based communication between PLCs and field sensors.
4️⃣ Future: Opta Hybrid Bridge
TCP master → Opta → RTU slave Opta acts as a gateway between Ethernet and serial Modbus networks.
🧩 Integration with Linux SDK
This Arduino SDK directly mirrors the Linux ModbusLite SDK’s internal architecture:
| Layer | Arduino SDK | Linux SDK | Purpose |
|---|---|---|---|
| Core Context | modbus_context.h | Same | Shared PDU/ADU state machine |
| TCP Transport | EthernetClient, EthernetServer | BSD sockets | Identical protocol framing |
| RTU Transport | Serial1 (RS485) | /dev/ttySx | CRC-compatible data exchange |
| High-Level API | ModbusLite | ModbusLite | Same class interface |
This ensures full cross-platform communication between Opta and Linux-based gateways.
🧱 Repository Structure
ModbusLite_Arduino/
├── src/
│ ├── ModbusLite.cpp
│ ├── ModbusLite.h
│ └── core/
│ ├── modbus_context.cpp
│ ├── modbus_tcp.cpp
│ ├── modbus_rtu.cpp
│ ├── modbus_server.cpp
│ ├── modbus_core.c
│ └── modbus_register_map.cpp
├── examples/
│ ├── Opta_TCP_Master/
│ ├── Opta_TCP_Slave/
│ ├── Opta_RTU_Master/
│ └── Opta_RTU_Slave/
└── README.md
⚙️ Requirements
- Arduino IDE 2.3.2+
- Opta board support package (Arduino-mbed 4.4.1+)
- Ethernet library (included with Opta BSP)
- RS485 shield or built-in port (Opta RS485 variant)
🧰 Installation
- Clone or download this repository into your Arduino libraries folder:
git clone https://github.com/vinayraj02/ModbusLite_Arduino- Open Arduino IDE → File → Examples → ModbusLite_Arduino
- Select your Opta board and upload one of the example sketches.
🧪 Testing
Use any of the following setups:
- 🖥️ QModMaster / Modbus Poll for PC-based TCP testing
- 🧩 Raspberry Pi with ModbusLite SDK as the TCP or RTU counterpart
- ⚙️ Two Opta boards for end-to-end industrial testing
🧮 Example Output
TCP Master Example
\=== Opta Modbus TCP Master ===
Local IP: 192.168.1.177
Connecting to Modbus slave...
\[OK\] Connected to Modbus slave.
Read Holding Registers:
Reg\[0\] = 29
Reg\[1\] = 10
Reg\[2\] = 20
Reg\[3\] = 30
Reg\[4\] = 40
\[OK\] Write success.
**RTU Slave Example**
\=== Opta Modbus RTU Slave ===
\[INFO\] RS485 initialized and listening...
\[INFO\] HoldingReg\[0\] = 42
\[INFO\] HoldingReg\[0\] = 43
📜 License
This library is licensed under the MIT License. See the LICENSE file for full details.
🤝 Contribution
Pull requests are welcome! If you find an issue, open a GitHub issue with:
- Your Opta board type
- Example sketch name
- Short description of the problem
All contributions that improve stability, performance, or Modbus compliance are encouraged.
🧭 Future Development
- 🔄 Hybrid TCP↔RTU gateway mode
- 🧰 Modbus diagnostics and hex frame monitor
- ⚡ Async callback support
- ☁️ Integration with Opta’s secure MQTT edge gateway layer
🤵 Maintained By
VK
Reliable • Lightweight • Cross-Platform
🏢 About ModbusLite SDK Family
The ModbusLite SDK family is a suite of robust, interoperable libraries designed for seamless Modbus communication across embedded and Linux environments.
- ModbusLite_Arduino: Tailored for Arduino Opta — lightweight and optimized for real-time industrial PLCs.
- ModbusLite Linux SDK: Full-featured for gateways, edge servers, and custom automation stacks on Raspberry Pi, Ubuntu, and beyond.
Both share a unified core architecture, ensuring zero-friction interoperability. Deploy Opta as a field controller alongside Linux-based orchestration — or bridge them effortlessly for hybrid networks. Built for reliability in mission-critical automation.