---
title: "Why W5300 connection speed only 10 MHz ?"
url: "https://maker.wiznet.io/forum/16005"
markdown_url: "https://maker.wiznet.io/forum/16005/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "szmentor"
created: "2026-03-17T19:06:20+09:00"
last_activity: "2026-03-20T08:56:58+09:00"
language: "en"
tags: ["C/C++"]
views: 3
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# Why W5300 connection speed only 10 MHz ?

## Question

Asked by szmentor on 2026-03-17 in Ethernet Chips.

W5300 has the PHYCR register ? HOW to set the speed 100MHZ

## Replies

### Reply 1 by TheoIm, 2026-03-20

W5300 does not provide a software-controlled PHY register such as PHYCR, unlike W6300.
Instead, the PHY operation mode is configured using hardware pins such as TEST_MODE and OP_MODE.
Please refer to Section 1.2 (Configuration Signals) of the W5300 datasheet for more details.
These configuration values are latched at hardware reset and cannot be changed during runtime.

If the “100MHz” mentioned in your question refers to 100BASE-TX (100 Mbps link speed),
this speed setting is not related to the MCU clock.
The Ethernet link speed is determined either by manually setting the OP_MODE pins
to select 100BASE-TX Full/Half Duplex, or by enabling auto-negotiation.

---

Source: https://maker.wiznet.io/forum/16005