---
title: "W5500 Ethernet PHY transceiver: Sharing the SPI bus with W5500 and an MFRC522"
url: "https://maker.wiznet.io/forum/16057"
markdown_url: "https://maker.wiznet.io/forum/16057/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "Kruparth"
created: "2026-04-23T21:08:21+09:00"
last_activity: "2026-04-27T10:26:58+09:00"
language: "en"
tags: ["W5500"]
views: 6
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W5500 Ethernet PHY transceiver: Sharing the SPI bus with W5500 and an MFRC522

## Question

Asked by Kruparth on 2026-04-23 in Ethernet Chips.

We have a requirement of adding an Ethernet support on our project but unfortunately we do not have addition SPI available so we just trying to check the feasibility of the sharing SPI bus with W5500 and MFRC522, both can operate on same SPI mode - 0, it although worked but after couple of hours, the ethernet drop the connectivity and never recovers. The W5500 driver throws error that it can't read from the W5500 registers. Controller we use is ESP32S3 and we develop with espressif's esp-idf framework.

We also tweaked the register timeout parameter in the W5500 increasing it to 500mS from 50mS, but still it fails.

All and all, is it a good idea to share an ethernet PHY transceiver with another low speed SPI device? We run both the SPI slaves at 1 MHz clock, Mode0 and the espressif's SPI HAL is thread-safe.

## Replies

### Reply 1 by TheoIm, 2026-04-27

Hi,

When sharing the same SPI bus, it is important to verify whether the **CS timing margins (setup/hold)** are properly maintained at the moment MISO data is being driven. This should be checked using an oscilloscope or logic analyzer.

In theory, this configuration is feasible. However, when issues occur, they are typically caused by **CS timing violations or MISO line contention**.

If the problem can be reproduced, it would be very helpful if you could capture and share the following signals:

- SPI CS (for each slave device)

- MISO

- MOSI

- SCLK

Additionally, if you have a case where the system operates normally, please provide the corresponding code or SPI control method. This will help with comparative analysis.

Thank you

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Source: https://maker.wiznet.io/forum/16057