---
title: "Issue with access to some W5500 registers"
url: "https://maker.wiznet.io/forum/15779"
markdown_url: "https://maker.wiznet.io/forum/15779/md"
type: "Forum topic"
category: "IO Modules"
author: "dgoffin"
created: "2025-06-25T16:09:42+09:00"
last_activity: "2025-06-27T15:13:51+09:00"
language: "en"
views: 5
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# Issue with access to some W5500 registers

## Question

Asked by dgoffin on 2025-06-25 in IO Modules.

To test the reliability of the SPI communication between the microcontroller EFM8LB12 and the module W5500io, I execute several reading and writing commands on different registers of the W5500. The SPI/SCLK frequency used is 12MHz.
The reading of all Common and Sockets registers gives the reset values found in the datasheet.
I use always the Variable Data Length mode.

For example, when I read the common registers [0x0009-0x000E], I find the correct Source Hardware Address written on the PCB of the module.
After reset, when I read the socket0 Destination Hardware Address registers [0x0006-0x000B], I find the reset value written in the datasheet : 0xFFFFFFFFFFFF. This is correct.
After having written [0x13-0x88] in the socket0 Source Port Register[0x0004-0x0005], I find the same value after a reading command. This is correct.

But after having written the values [0x08-0xDC-0x00-0x01-0x02-0x0A] in the socket0 Destination Hardware Address registers [0x0006-0x000B], I read the values [0xFF-0xFF-0xFF-0xFF-0xFF-0xFF]. The writing does not work.
It is the same issue for other registers like Socketn Destination IP Address Register which remains [0x00000000] after writing anything…
I don't understand why the issue is limited to only some registers like those explained above.

Thanks for an answer.

## Replies

### Reply 1 by Aimee0, 2025-06-27

Thank you for your inquiry. To help diagnose the issue, please check the following points:

**Are you using the latest version of WIZnet’s ioLibrary?**
Older versions may contain bugs related to register access. Please ensure you are using the most recent release from the [WIZnet GitHub repository](https://github.com/WIZnet/ioLibrary_Driver).

**Have you completed all necessary initialization steps for the WIZnet chip before accessing the common registers?Make sure your SPI communication is set to Mode 0 or Mode 3 only.**
W5500 supports only SPI Mode 0 and Mode 3. Using other modes may result in incorrect timing and communication failures.

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Source: https://maker.wiznet.io/forum/15779