---
title: "How Do W55MH32 and W5500 Registers Enable Bare-Metal TCP Communication?"
url: "https://maker.wiznet.io/Arnold/projects/how-do-w55mh32-and-w5500-registers-enable-bare-metal-tcp-communication/"
markdown_url: "https://maker.wiznet.io/Arnold/projects/how-do-w55mh32-and-w5500-registers-enable-bare-metal-tcp-communication/md"
type: "UCC: User Created Content"
author: "Arnold"
author_url: "https://maker.wiznet.io/Arnold/"
original_author: "Jacen_Xu"
original_url: "https://www.cnblogs.com/bitconn/p/18922145"
license: "Apache License 2.0 (Apache-2.0)"
published: "2026-01-30"
language: "en"
likes: 0
views: 243
comments: 0
source: "WIZnet Makers (https://maker.wiznet.io/)"
---

# How Do W55MH32 and W5500 Registers Enable Bare-Metal TCP Communication?

> How Do W55MH32 and W5500 Registers Enable Bare-Metal TCP Communication?

Original author: Jacen_Xu (source: https://www.cnblogs.com/bitconn/p/18922145)

## Article

## How Do W55MH32 and W5500 Registers Enable Bare-Metal TCP Communication?

### Register, Buffer, and Socket Lifecycle Understanding for Reliable Ethernet Firmware

**(W55MH32와 W5500 레지스터는 베어메탈 TCP 통신을 어떻게 가능하게 하는가?)**

---

### Summary (40–60 words)

This article explains how the W55MH32 MCU works with the WIZnet W5500 Ethernet controller at the register and buffer level to implement TCP communication on bare-metal systems. By understanding SPI access patterns, TX/RX buffer management, and the hardware TCP socket lifecycle, developers can build reliable Ethernet firmware without complex software TCP/IP stacks.

---

### 1. Why Register-Level Understanding Still Matters

In many embedded projects, Ethernet is treated as a “black box” behind libraries.
However, on **bare-metal systems**, long-term stability depends on understanding:

How registers are accessed over SPI

How TX/RX buffers are organized

How TCP sockets transition through states

The **W55MH32 + W5500** combination is a classic example where:

> **Understanding the hardware design directly translates to simpler, more reliable firmware.**

---

### 2. System Architecture Overview

#### Bare-Metal Ethernet Architecture

`Application Logic (Bare-Metal) ↓ W5500 Driver Logic ↓ SPI Interface (W55MH32) ↓ W5500 Register & Buffer Blocks ↓ Hardware TCP/IP Engine ↓ Ethernet PHY (RJ45) `

Key architectural property:

**No software TCP/IP stack exists on W55MH32**

TCP/IP is fully implemented in W5500 hardware

Firmware controls the network entirely through registers

---

### 3. SPI Access Model of W5500

Every interaction with the W5500 happens via **SPI frames**, consisting of:

**16-bit address** (block offset)

**Control byte**

Block select

Read/write flag

Variable or fixed data mode

**Data bytes**

#### Why This Matters

SPI framing defines **atomic operations**.
Breaking a frame incorrectly causes:

Corrupted register writes

Invalid buffer pointers

Silent TCP failures

A correct driver enforces:

> **One logical operation = one CS assertion**

---

### 4. W5500 Register Blocks and Their Roles

W5500 internally divides memory into logical blocks:

**Common Registers**

MAC address

IP address

Gateway, subnet

Interrupt configuration

**Socket Registers (8 identical sets)**

Mode (TCP/UDP)

Port numbers

Destination IP/port

Command & status registers

**TX Buffers / RX Buffers**

16 KB TX shared

16 KB RX shared

Understanding this structure eliminates guesswork.

---

### 5. TX/RX Buffer Model: Why TCP Becomes Simple

Unlike software stacks, W5500 exposes TCP buffers directly.

#### TX Path (Conceptual)

`Application Data ↓ Write to TX Buffer ↓ Update TX Write Pointer ↓ SEND Command ↓ Hardware TCP Transmission `

#### RX Path (Conceptual)

`Packet Arrives ↓ RX Size Register Updated ↓ Read from RX Buffer ↓ Update RX Read Pointer ↓ RECV Command `

Key insight:

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

---

### 6. TCP Socket Lifecycle in Hardware

Each W5500 socket implements a full TCP state machine:

`CLOSED → INIT → LISTEN / SYNSENT → ESTABLISHED → FIN_WAIT / CLOSE_WAIT → CLOSED `

On bare-metal firmware:

W55MH32 **does not manage TCP states**

It only:

Writes socket commands

Polls status registers

Moves buffer pointers

This dramatically reduces firmware complexity.

---

### 7. Typical Bare-Metal TCP Flow (W55MH32)

Initialize SPI

Configure W5500 common registers

Allocate socket and set TCP mode

Issue CONNECT or LISTEN command

Wait for `ESTABLISHED` state

Send and receive data via buffers

Close socket cleanly

At no point is TCP logic implemented in software.

---

### 8. Common Failure Modes (And Why They Happen)

#### ❌ SEND returns OK, but no data received

Cause:

TX pointer not updated correctly

SPI transaction split across CS boundaries

#### ❌ RX size shows data, but read fails

Cause:

RX read pointer not advanced

RECV command not issued

#### ❌ Socket stuck in CLOSE_WAIT

Cause:

Firmware never processes remaining RX data

All these issues disappear when register and buffer semantics are respected.

---

### 9. Why This Design Is Ideal for Bare-Metal Systems

For W55MH32-based systems:

No RAM wasted on TCP/IP stacks

No timing jitter from software TCP

Predictable behavior

Easy debugging with logic analyzer

This makes the architecture suitable for:

Industrial controllers

Networked sensors

Long-running embedded devices

---

### 10. Key Takeaway

> **On bare-metal systems, W5500 turns TCP from a software problem into a register-management problem—and that is a good thing.**

Once developers understand:

SPI framing

Register blocks

Buffer pointer rules

TCP and UDP communication become straightforward and reliable.

---

### FAQ (Engineer-Focused)

**Q1. Does W55MH32 run TCP/IP code?**
No. All TCP/IP logic is inside the W5500.

**Q2. Is register-level programming required?**
Yes for bare-metal, but it greatly simplifies reliability.

**Q3. How many TCP connections are supported?**
Up to 8 hardware sockets.

**Q4. Is this approach faster than software TCP/IP?**
Yes, and far more deterministic.

**Q5. Is this suitable for industrial products?**
Absolutely—this is where it excels.

---

### Source

CNBlogs article (bitconn)

WIZnet W5500 Datasheet

WIZnet W55MH32 documentation

---

### Tags

W55MH32, W5500, WIZnet, Register-Level Ethernet, TCP Socket Lifecycle, SPI Driver, Bare-Metal Networking, Industrial Ethernet

---

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## 🇰🇷 한국어 번역 (1:1 Full Translation)

---

## W55MH32와 W5500 레지스터는 베어메탈 TCP 통신을 어떻게 가능하게 하는가?

### 레지스터·버퍼·소켓 생명주기로 이해하는 이더넷 펌웨어 설계

---

### 요약

본 문서는 W55MH32 MCU와 WIZnet W5500 이더넷 컨트롤러를 사용한 베어메탈 TCP 통신 구조를 설명한다. SPI 접근 방식, TX/RX 버퍼 관리, 하드웨어 TCP 소켓 생명주기를 이해함으로써, 복잡한 소프트웨어 TCP/IP 스택 없이도 안정적인 이더넷 펌웨어를 구현할 수 있음을 보여준다.

---

### 1. 왜 레지스터 수준 이해가 중요한가

베어메탈 환경에서는
하드웨어 동작을 정확히 이해하는 것이 안정성의 핵심이다.

---

### 2. 시스템 아키텍처

`애플리케이션 ↓ W5500 드라이버 ↓ SPI ↓ W5500 하드웨어 TCP/IP `

TCP는 소프트웨어가 아닌 하드웨어가 처리한다.

---

### 3. SPI 프레임 모델

SPI 프레임은 원자적이어야 하며
CS 분리는 허용되지 않는다.

---

### 4. 레지스터 블록 구조

공통 레지스터

소켓 레지스터

TX/RX 버퍼

---

### 5. 버퍼 기반 TCP 처리

포인터 관리만 정확하면
TCP 신뢰성은 자동으로 보장된다.

---

### 6. TCP 소켓 생명주기

소켓 상태 전이는
모두 W5500 하드웨어에서 수행된다.

---

### 7. 베어메탈 TCP 흐름

초기화 → 연결 → 송수신 → 종료

---

### 8. 대표적인 오류 원인

CS 타이밍 오류

포인터 미갱신

RECV 누락

---

### 9. 산업용 적합성

예측 가능한 동작

장시간 안정성

낮은 메모리 사용량

---

### 10. 핵심 메시지

> **W5500은 TCP를 소프트웨어 문제가 아닌 레지스터 관리 문제로 바꾼다.**

---

### 태그

W55MH32, W5500, WIZnet, 베어메탈 TCP, 레지스터 기반 이더넷, 산업용 네트워크

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Source: https://maker.wiznet.io/Arnold/projects/how-do-w55mh32-and-w5500-registers-enable-bare-metal-tcp-communication/