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+# DN23E08 Modbus Slave
+
+This project enables the DN23E08, an Arduino-based PLC module, to function as a Modbus RTU slave device, allowing it to be integrated into industrial automation systems and controlled remotely via Modbus communication.
+
+## Features
+
+- **Modbus RTU Slave**: Implements standard Modbus RTU protocol over RS485
+- **I/O Mapping**: Maps DN23E08 inputs/outputs to Modbus registers
+- **Arduino-based**: Easy to customize and extend using Arduino IDE
+
+## Hardware Requirements
+
+- DN23E08 PLC module
+- Arduino Nano v3.0 (required for DN23E08 operation)
+- RS485 communication interface
+- 12-24V power supply
+
+## Installation
+
+1. Clone this repository:
+   ```bash
+   git clone https://git.nielsgeens.be/projects/DN23E08_modbus.git
+   cd DN23E08_modbus
+   ```
+
+2. Open the Arduino sketch in Arduino IDE
+
+3. Install required libraries (if any - check the code for dependencies)
+
+4. Configure your Modbus settings:
+   - Slave ID
+   - Baud rate
+   - Parity settings
+
+5. Upload the sketch to your Arduino Nano
+
+## Configuration
+
+Edit the configuration parameters in the main sketch:
+
+```cpp
+// Modbus Configuration
+#define SLAVE_ID 1          // Modbus slave address
+#define BAUD_RATE 9600      // RS485 baud rate
+#define PARITY SERIAL_8N1   // Parity settings
+```
+
+## Modbus Register Map
+
+| Register Type | Address Range | Description |
+|---------------|---------------|-------------|
+| Coils | 0x0000-0x0007 | Digital outputs (relays) |
+| Discrete Inputs | 0x0000-0x0007 | Digital inputs (opto-isolated) |
+| Input Registers | 0x0000-0x0007 | Analog inputs (current/voltage) |
+| Holding Registers | 0x0000-0x00FF | Configuration and control registers |
+
+## Usage
+
+1. Connect the DN23E08 to your Modbus master via RS485
+2. Configure your Modbus master with the correct slave ID and communication settings
+3. Use standard Modbus function codes to read inputs and write outputs:
+   - **Read Coils (0x01)**: Read relay output status
+   - **Read Discrete Inputs (0x02)**: Read digital input status
+   - **Read Input Registers (0x04)**: Read analog input values
+   - **Write Single Coil (0x05)**: Control individual relay outputs
+   - **Write Multiple Coils (0x0F)**: Control multiple relay outputs