---
title: "W6300-based 2-port Ethernet setup on the RP2350 (loopback example)"
url: "https://maker.wiznet.io/Lihan__/projects/w6300-based-2-port-ethernet-setup-on-the-rp2350-loopback-example/"
markdown_url: "https://maker.wiznet.io/Lihan__/projects/w6300-based-2-port-ethernet-setup-on-the-rp2350-loopback-example/md"
type: "WCC: WIZnet Created Content"
author: "Lihan__"
author_url: "https://maker.wiznet.io/Lihan__/"
original_author: "Lihan"
published: "2025-05-27"
language: "en"
likes: 0
views: 1903
comments: 0
source: "WIZnet Makers (https://maker.wiznet.io/)"
---

# W6300-based 2-port Ethernet setup on the RP2350 (loopback example)

> This project explains how to configure dual Ethernet interfaces on the RP23450 using the W6300 and ioLibrary, and also presents a loopback test example with the

Original author: Lihan

## Documents and links

- [WIZnet-PICO-C_2port_W6300](https://github.com/seok930927/WIZnet-PICO-C_2port_W6300) (code): forked from WIZnet-ioNIC/WIZnet-PICO-C

## Article

**PROJECT DESCRIPTION**

## Setting up 2-ports Ethernet on the RP2350 using the W6300 and Iolibrary

In this project, we focus on controlling two W6300 Ethernet chips using the ioLibrary.

By default, the ioLibrary provided by WIZnet is designed to handle only one WIZchip at a time. It doesn’t natively support multi-chip setups, so we had to modify parts of the library to make it work with multiple W6300s.

We also walk through how to design the circuit to properly connect two W6300 chips to the RP2350, covering both hardware considerations and practical implementation tips.

## 🔌 Circuit Configuration

For this project, we used the following hardware components:

- **W6300-EVB-Pico2**

- **WIZ630io**

![](https://maker.wiznet.io/upload/ckeditor5/658834093%5F1748356993%2Epng)

The two W6300 chips **share the SPI data lines and clock signal (CLK)**, while the **chip select (CS)** and **reset (RST)** pins are connected to **separate GPIOs** on the RP2350.

This configuration allows both chips to operate on the same SPI bus, with independent control over selection and reset via software.

![](https://maker.wiznet.io/upload/ckeditor5/658834093%5F1748358332%2Epng)

## 🧩 A Simple Trick to Use Two W6300 Chips

In this project, the main goal was to use **two W6300 Ethernet chips** while making **minimal changes to the existing ioLibrary**.

Here’s how we approached it:

1. The **first W6300** uses **socket numbers 0–7**, just like before.

2. The **second W6300** is assigned **virtual socket numbers 8–15**.

This way, it feels like the system supports **16 sockets in total**.

---

## ⚠️ The Problem

Internally, W6300 uses something called the **BSB field** to select socket registers.
However, this field is **only 3 bits wide**, meaning it can represent **socket numbers 0–7 only**.

![](https://maker.wiznet.io/upload/ckeditor5/658834093%5F1748361073%2Epng)
So technically, using socket numbers 8–15 is not allowed and would generate **invalid register values**.

---

## 🔧 How We Solved It

Luckily, the structure of the ioLibrary makes this possible.

Actual SPI communication happens in the following functions:

```plaintext
read_byte(opcode, ...); 
write_byte(opcode, ...);
```

The R/W bit isn’t important until just before the SPI signal is transmitted.
As long as it's set correctly at that final step, everything works fine.

![](https://maker.wiznet.io/upload/ckeditor5/658834093%5F1748360744%2Epng)

So here’s the trick:

- We temporarily pretend that sockets 0–15 are valid throughout the upper layers of the code.

- Just before the SPI command is sent, we:

1. **Clear the RWB bit** in the opcode at the beginning.

2. **Check the socket number and the RWB bit**:
  - If `RWB == 0` and socket number is `0–7`: select **W6300 #0** (CS0)
  - If `RWB == 1` and socket number is `8–15`: select **W6300 #1** (CS1)

3. **Set the RWB bit properly** according to whether it's a read or write operation.

We also **borrow 1 bit (the R/W bit)** to expand the socket range internally, giving us **4 usable bits** in total. That’s how we distinguish between the two chips.

---

## ✅ The Result

From the application’s perspective, you just need to assign socket numbers from **0 to 15**.

Internally, the system **automatically selects the correct chip** and **sets up the right SPI command**.

The ioLibrary remains **almost untouched**.

### loopback TEST

The following log shows the initialization of two W6300 chips,
where each chip is assigned a unique IP address and a loopback server is opened on both.

![](https://maker.wiznet.io/upload/ckeditor5/658834093%5F1748361821%2Epng)

The next screenshot shows the actual **loopback communication in action**,
demonstrating successful data transmission and reception.

![](https://maker.wiznet.io/upload/ckeditor5/658834093%5F1748361971%2Epng)

---

Source: https://maker.wiznet.io/Lihan__/projects/w6300-based-2-port-ethernet-setup-on-the-rp2350-loopback-example/