---
title: "How Does a TCP Server Work on W5500-EVB-PICO?"
url: "https://maker.wiznet.io/chen/projects/how-does-a-tcp-server-work-on-w5500-evb-pico/"
markdown_url: "https://maker.wiznet.io/chen/projects/how-does-a-tcp-server-work-on-w5500-evb-pico/md"
type: "UCC: User Created Content"
author: "诗然小筑"
author_url: "https://www.bilibili.com/video/BV1wx4y1C7ty/?spm_id_from=333.1387.upload.video_card.click&vd_source=ab013cc5ffdecedae5ee47ae256d7306"
editor: "WIZnet"
editor_url: "https://maker.wiznet.io/"
original_author: "诗然小筑"
original_url: "https://www.bilibili.com/video/BV1wx4y1C7ty/?spm_id_from=333.1387.upload.video_card.click&vd_source=ab013cc5ffdecedae5ee47ae256d7306"
published: "2026-01-30"
language: "en"
likes: 0
views: 276
comments: 0
source: "WIZnet Makers (https://maker.wiznet.io/)"
---

# How Does a TCP Server Work on W5500-EVB-PICO?

> This article explains how a TCP server is implemented on the W5500-EVB-PICO using the WIZnet W5500 Ethernet controller.

Original author: 诗然小筑 (source: https://www.bilibili.com/video/BV1wx4y1C7ty/?spm_id_from=333.1387.upload.video_card.click&vd_source=ab013cc5ffdecedae5ee47ae256d7306)

## Article

## How Does a TCP Server Work on W5500-EVB-PICO?

### An End-to-End TCP Protocol Workflow Using Hardware TCP/IP

**(W5500-EVB-PICO에서 TCP 서버는 어떻게 동작하는가?)**

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### Summary (40–60 words)

This article explains how a TCP server is implemented on the W5500-EVB-PICO using the WIZnet W5500 Ethernet controller. By walking through the complete TCP server workflow—from socket initialization to connection handling and data exchange—it shows how hardware TCP/IP offloading enables predictable, reliable server behavior on embedded systems.

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### 1. Why a TCP Server Demo Matters for Embedded Engineers

TCP servers are often treated as “PC-side” concepts, but in embedded systems they are critical for:

Device control interfaces

Configuration tools

Diagnostics and testing

Industrial equipment communication

For engineers, the challenge is not the TCP protocol itself, but **how TCP behaves when implemented on constrained hardware**.

The **W5500-EVB-PICO** provides a clean environment to observe:

> **How a hardware TCP/IP engine behaves as a real TCP server.**

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### 2. What Is W5500-EVB-PICO?

The W5500-EVB-PICO combines:

**RP2040 MCU** (dual-core Cortex-M0+)

**WIZnet W5500 Ethernet controller**

SPI-based MCU ↔ Ethernet interface

Key design principle:

RP2040 handles **application logic**

W5500 handles **TCP/IP entirely in hardware**

This makes the board ideal for **protocol workflow demonstrations**.

---

### 3. System Architecture Overview

#### TCP Server Architecture

`TCP Client (PC / Tool) ↓ Ethernet Network ↓ W5500 Hardware TCP/IP Engine ↓ SPI Interface ↓ RP2040 Application Logic `

Important separation:

No software TCP/IP stack runs on RP2040

All TCP state transitions occur inside W5500

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### 4. TCP Server Role on W5500

In a TCP server setup, the embedded device:

Listens on a fixed TCP port

Accepts incoming client connections

Exchanges data bidirectionally

Closes connections cleanly

On W5500, this behavior is driven by **socket registers and commands**, not software state machines.

---

### 5. End-to-End TCP Server Workflow

#### Step-by-Step Protocol Flow

`Power On ↓ W5500 Network Initialization ↓ Socket Open (TCP mode) ↓ LISTEN command ↓ Client connects ↓ Socket enters ESTABLISHED ↓ Data RX/TX ↓ Connection close ↓ Socket returns to CLOSED `

Each step corresponds directly to a W5500 socket register state.

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### 6. Socket Initialization and LISTEN State

To start a TCP server:

Select a hardware socket (0–7)

Set socket mode to TCP

Configure local port

Issue **LISTEN** command

At this point:

W5500 waits for incoming SYN packets

RP2040 simply polls socket status

No software TCP handshake is implemented.

---

### 7. Connection Establishment (Hardware-Driven)

When a client connects:

W5500 performs the TCP three-way handshake internally

Socket status changes to **ESTABLISHED**

An interrupt or status poll notifies the MCU

From the MCU’s perspective:

> A TCP connection “just appears” as ESTABLISHED.

This is a major simplification compared to software stacks.

---

### 8. Data Transmission and Reception

#### RX Path

`Client sends data ↓ W5500 stores data in RX buffer ↓ RX size register updated ↓ MCU reads RX buffer ↓ RX pointer updated ↓ RECV command issued `

#### TX Path

`MCU writes data to TX buffer ↓ TX pointer updated ↓ SEND command issued ↓ W5500 handles TCP transmission `

Key insight:

> **Once pointers are correct, TCP reliability is guaranteed by hardware.**

---

### 9. Connection Termination

When either side closes the connection:

W5500 transitions through FIN states

Socket eventually returns to CLOSED

Firmware can re-enter LISTEN

Correctly handling RX data before closing is critical to avoid CLOSE_WAIT issues.

---

### 10. Why This TCP Server Model Is Reliable

Compared to software TCP servers, this design offers:

Deterministic behavior

No retransmission logic in firmware

Minimal RAM usage

Easy debugging via registers

For engineers, TCP becomes **observable and predictable**.

---

### 11. Typical Use Cases

PC-based test tools connecting to embedded devices

Industrial control panels

Debug consoles over Ethernet

Simple device-to-device TCP protocols

The W5500 TCP server is especially well suited for **long-running systems**.

---

### 12. Key Takeaway

> **On W5500-EVB-PICO, a TCP server is implemented by controlling socket states and buffers—not by writing a TCP stack.**

This allows engineers to:

Focus on application logic

Trust hardware for protocol correctness

Build reliable Ethernet servers with minimal code

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### FAQ (Engineer-Focused)

**Q1. Does RP2040 implement TCP logic?**
No. TCP is fully handled by the W5500.

**Q2. How many TCP clients can connect?**
Up to 8, limited by socket availability.

**Q3. Is this suitable for industrial use?**
Yes. Deterministic behavior makes it ideal.

**Q4. What happens if the client disconnects unexpectedly?**
W5500 handles TCP cleanup automatically.

**Q5. Why use a TCP server instead of UDP?**
TCP provides reliable, ordered delivery.

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### Source

Bilibili video: **BV1wx4y1C7ty**

WIZnet W5500 Datasheet

W5500-EVB-PICO documentation

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### Tags

W5500, WIZnet, TCP Server, W5500-EVB-PICO, Embedded Ethernet, Hardware TCP/IP, Industrial Networking

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## 🇰🇷 한국어 번역 (1:1 Full Translation)

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## W5500-EVB-PICO에서 TCP 서버는 어떻게 동작하는가?

### 하드웨어 TCP/IP 기반 TCP 서버 프로토콜 워크플로우

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### 요약

본 문서는 WIZnet W5500 이더넷 컨트롤러가 탑재된 W5500-EVB-PICO에서 TCP 서버를 구현하는 과정을 설명한다. 소켓 초기화부터 연결 수립, 데이터 송수신, 연결 종료까지의 전체 TCP 워크플로우를 통해, 하드웨어 TCP/IP 오프로딩이 임베디드 시스템에서 어떻게 안정적인 서버 동작을 제공하는지를 분석한다.

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### 1. TCP 서버 데모의 의미

임베디드 시스템에서 TCP 서버는
제어, 설정, 테스트 인터페이스로 매우 중요하다.

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### 2. W5500-EVB-PICO 개요

RP2040은 애플리케이션을 담당하고
TCP/IP는 W5500이 처리한다.

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### 3. 시스템 아키텍처

`TCP 클라이언트 ↓ W5500 하드웨어 TCP/IP ↓ RP2040 애플리케이션 `

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### 4. TCP 서버 동작 흐름

LISTEN → ESTABLISHED → DATA → CLOSED

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### 5. 데이터 송수신

버퍼 포인터만 정확하면
TCP 신뢰성은 자동으로 보장된다.

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### 6. 산업용 관점

예측 가능한 네트워크

장시간 안정성

간단한 펌웨어

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### 7. 핵심 메시지

> **W5500 기반 TCP 서버는 소프트웨어 TCP 구현이 아닌, 소켓 제어 문제다.**

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### 태그

W5500, TCP 서버, W5500-EVB-PICO, 임베디드 이더넷, 하드웨어 TCP/IP

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Source: https://maker.wiznet.io/chen/projects/how-does-a-tcp-server-work-on-w5500-evb-pico/