---
title: "Can you just explain the XI and XO pins on the W5500 for me?"
url: "https://maker.wiznet.io/forum/15306"
markdown_url: "https://maker.wiznet.io/forum/15306/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "matthewu"
created: "2024-10-16T03:01:11+09:00"
last_activity: "2024-10-16T03:01:11+09:00"
language: "en"
tags: ["W5500"]
views: 4
replies: 0
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# Can you just explain the XI and XO pins on the W5500 for me?

## Question

Asked by matthewu on 2024-10-16 in Ethernet Chips.

So I have a circuit that is using the W5500 and I'm using this oscillator: <https://www.digikey.com/en/products/detail/cts-frequency-controls/CB3LV-5I-25M000000/663671>

When I connect the EOH pin (enable) to the XO pin on the W5500 it no longer works, but if I leave it floating it's fine. I read the datasheet and that is apparently explained in the XI section:

> Crystal input / External Clock input External 25MHz Crystal Input. This pin can also be connected to single-ended TTL oscillator (CLKIN). 3.3V clock should be applied for the External Clock input. If this method is implemented, XO should be left unconnected. Refer to the ‘Crystal reference schematic’ (Figure.3) for details.

Then for XO:

> Crystal output External 25MHz Crystal Output Note: Float this pin if using an external clock being driven through XI/CLKIN

Pardon me for my ignorance, but this is very confusing to me. It may be because I am new to the PCB world. I feel like I missed something entirely.

I figured that XO would just go high when I wanted the oscillator to run and low when I didn't need it, then the output of the oscillator came back through XI. Obviously it's more complicated than that. Can anyone break this down for me? There isn't really anything else to it in the datasheet.

Thanks.

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Source: https://maker.wiznet.io/forum/15306