--- title: "Arduino + W5500 Ethernet Series Overview (C & Modbus TCP)" url: "https://maker.wiznet.io/irina/projects/arduino-w5500-ethernet-series-overview-c-modbus-tcp/" markdown_url: "https://maker.wiznet.io/irina/projects/arduino-w5500-ethernet-series-overview-c-modbus-tcp/md" type: "UCC: User Created Content" author: "녹칸다" author_url: "https://www.youtube.com/watch?v=kBNqc-gWM-A&t=1s" editor: "WIZnet" editor_url: "https://maker.wiznet.io/" original_author: "녹칸다" original_url: "https://www.youtube.com/watch?v=kBNqc-gWM-A&t=1s" published: "2025-09-25" language: "en" tags: ["W5500", "Arduino"] likes: 0 views: 2458 comments: 0 source: "WIZnet Makers (https://maker.wiznet.io/)" --- # Arduino + W5500 Ethernet Series Overview (C & Modbus TCP) > Nokanda’s Arduino + W5500 series evolves from Ethernet basics to Modbus TCP, showing step-by-step networking, request/response, and protocol use. Original author: 녹칸다 (source: https://www.youtube.com/watch?v=kBNqc-gWM-A&t=1s) ## Article **Clicking the picture redirects you to the maker’s website.** | [![](https://maker.wiznet.io/upload/ckeditor5/447089944%5F1758793266%2Epng)](https://maker.wiznet.io/bruno/projects/610%2Darduino%2Dw5500%2D%2D%2Dethernet%2D%2Dc%2D%2D%2D%2D%2D%2D2/) | [![](https://maker.wiznet.io/upload/ckeditor5/447089944%5F1758793255%2Epng)](https://maker.wiznet.io/bruno/projects/611%2Darduino%2D%2Dethernet%2D%2Dc%2D%2D%2D%2D%2D%2D%2D2/) | [![](https://maker.wiznet.io/upload/ckeditor5/447089944%5F1758793243%2Epng)](https://maker.wiznet.io/bruno/projects/612%2Darduino%2Dw5500%2D%2Dc%2Drequest%2Dresponse%2D%2D%2D%2D%2D%2D2/) | [![](https://maker.wiznet.io/upload/ckeditor5/447089944%5F1758793307%2Epng)](https://maker.wiznet.io/irina/projects/614%2Darduino%2Dw5500%2D%2Dc%2D%2Dmodbus%2Dtcp%2D%2D%2D%2D%2D%2D%2D%2D%2D2/) | [![](https://maker.wiznet.io/upload/ckeditor5/447089944%5F1758793321%2Epng)](https://maker.wiznet.io/irina/projects/615%2Darduino%2Dw5500%2D%2Dc%2D%2Dmodbus%2Dtcp%2D%2D%2D%2D%2D%2D%2D%2D%2D2/) | | --- | --- | --- | --- | --- | ## 1. Introduction This post collects and explains a full **Arduino + W5500 Ethernet series**. The videos are** created by Nokanda**, with project posts shared by different contributors: He uploaded the fundamentals** (#610, #611, #612)**. He uploaded the applied part **(#614,# 615)** to extend the series into Modbus TCP. ➡️ Readers can learn step by step: **networking basics → request/response → Modbus TCP fundamentals → advanced Modbus TCP features**. #614, #615 goes beyond a simple Modbus TCP example and demonstrates **practical implementation with Arduino UNO + W5500 Ethernet**. We start with the basics: controlling and reading coils with **FC05 (Write Single Coil)** and **FC01 (Read Coils)**, and then expand to advanced functions such as **FC15 (Write Multiple Coils)**, **FC06 (Write Single Register)**, and **FC04 (Read Input Registers)** including **32-bit floating-point data**. Arduino acts as a **Modbus TCP Slave (Server)**, while the C# WinForms application functions as the **Master (Client)**. #### Series Roadmap Diagram ```plaintext [Networking Basics] (610, 611) by Bruno ↓ [Request/Response] (612) by Bruno ↓ [Modbus TCP Basics] (614) by irina ↓ [Modbus TCP Advanced] (615) by irina Videos created by Nokanda ``` --- ![](https://maker.wiznet.io/upload/ckeditor5/447089944%5F1758793590%2Epng) ### 3. Modbus TCP 프레임구조 ```plaintext +--------------------------------------+ | MBAP Header (7 bytes) | | - Transaction ID (2) | | - Protocol ID (2) | | - Length (2) | | - Unit ID (1) | +---------------------------------------+ | PDU | | - Function Code (1) | | - Data (N) | +---------------------------------------+ ``` ## 2. Modbus RTU vs TCP **RTU** - Requires CRC16 checksum - RS-485/RS-232 based - 1-byte slave address **TCP** - CRC removed (error handling by TCP/IP) - Adds a 6-byte **MBAP Header** - Devices identified by **IP address** instead of only Slave ID 👉 Conclusion: **TCP is more scalable and network-friendly**, making it better suited for industrial control and IoT. --- ## 3. Modbus Basics - **Coils:** 1-bit (ON/OFF, mapped to Arduino GPIO pins) - **Registers:** 16-bit values (used for variables or sensor data) - **Common Function Codes:** - `0x01` → Read Coils (#614) - `0x05` → Write Single Coil (#614) - `0x15` → Write Multiple Coils (#615) - `0x06` → Write Single Register (#615) - `0x04` → Read Input Registers (32-bit float supported, #615) --- ## 4. Arduino + W5500 Examples #### (1) Write Single Coil (FC05, #614) Control a single LED (Coil0 → D2). ```plaintext ON → 00 01 00 00 00 06 01 05 00 00 FF 00 OFF → 00 01 00 00 00 06 01 05 00 00 00 00 ``` #### (2) Read Coils (FC01, #614) Read multiple coil states and display them in the UI. #### (3) Write Multiple Coils (FC15, #615) Batch control multiple LEDs (Coil0~Coil5 → D2~D7). #### (4) Write Single Register (FC06, #615) Update Arduino’s variable remotely with a 16-bit value. #### (5) Read Input Registers (FC04, #615) Read sensor values or variables. 32-bit float = 2 registers (4 bytes) Must agree on **endianness and word order** (ABCD, BADC, CDAB, DCBA). --- ## 5. C# WinForms UI Integration - Acts as **Modbus TCP Master**. - Supports: - Coil ON/OFF buttons - Register write/read - Timer-based real-time coil monitoring - Implementation: - **Raw Socket:** Build MBAP + PDU manually - **NModbus4 Library:** Simplifies request/response handling - Always include timeout, retry logic, and exception frame parsing (FC | 0x80). --- ## 6. Troubleshooting - **Endian mismatch:** Garbage float values - **Length mismatch:** Master rejects frame - **Coil bit packing error:** Wrong LED toggles - **W5500 buffer overflow (2KB/socket):** Frame truncation → use shorter packets --- ## 7. Conclusion **#614:** Focused on basics — single coil write (FC05) and coil read (FC01). **#615:** Extended to advanced control — multiple coil writes (FC15), register writes (FC06), and safe float data exchange with FC04. 👉 The combination of **Arduino UNO + W5500 Ethernet (slave)** and **C# WinForms (master)** provides a **practical Modbus TCP solution** for: - Industrial control - IoT gateways - Remote monitoring systems --- ## ✅ Key SEO Keywords Arduino Modbus TCP W5500 Ethernet module Modbus RTU vs TCP differences C# WinForms Modbus example FC15 multiple coil write FC06 single register write FC04 read input registers 32-bit float Modbus data ➡️ Next, I plan to explore **TLS security, MQTT bridging, and cloud integration** as future extensions. --- Source: https://maker.wiznet.io/irina/projects/arduino-w5500-ethernet-series-overview-c-modbus-tcp/