---
title: "W55RP20 multi client Modbus TCPIP server"
url: "https://maker.wiznet.io/forum/15730"
markdown_url: "https://maker.wiznet.io/forum/15730/md"
type: "Forum topic"
category: "MCU & Boards"
author: "a_davi"
created: "2025-05-16T01:34:15+09:00"
last_activity: "2025-05-20T12:20:44+09:00"
language: "en"
views: 11
replies: 2
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W55RP20 multi client Modbus TCPIP server

## Question

Asked by a_davi on 2025-05-16 in MCU & Boards.

Hi we have a successful product built on the w5500-evb-pico. This is a Modbus RTU to TCP converter. The w55rp20 acts as a server and must accept at least 2 clients. We now use the:-

1. W55RP20lwIP library

2. ArduinoModbus library

The w55rp20 works just fine for single client but does not accept the second one. If I turn off the first one the second one connects and works fine. Does not work simultaneously.

for the w5500-evb-pico we used

1. Ethernet library

2. ArduinoModbus library

This works just fine for 2 clients simultaneously.

Any pointers for me what I should be doing?

Thanks Amit

## Replies

### Reply 1 by a_davi, 2025-05-16

Unfortunately the Ethernet Library is not compatible with the w55rp20 as the W5500 chip is not mapped to a SPI port instead mapped to a PIO.

Any advise?

Amit

### Reply 2 by Lihan__, 2025-05-20

Is the following an accurate summary of your setup?

**Client (W5500-EVB-Pico)** — Working as expected
→ Using the `Ethernet` library
→ Using the `ArduinoModbus` library

**Server (W55RP20)** — Only one client can connect
→ Using the `W55RP20lwIP` library
→ Using the `ArduinoModbus` library

For case, (Server with W55RP20), may I ask why you're using lwIP?

When using lwIP with W55RP20, it typically operates in **MACRAW mode**, which means **only socket 0 is available**.

To support multiple clients, you’ll need to use the **hardware TCP/IP offload engine (TOE)** available on W5500 and W55RP20, which allows access to **all 8 hardware sockets**.

We’re having a bit of trouble understanding your additional message.

> ***Unfortunately the Ethernet Library is not compatible with the w55rp20 as the W5500 chip is not mapped to a SPI port instead mapped to a PIO. ***

1. Are you trying to connect the W55RP20 and W5500 via SPI? (Could you please share the specific interface configuration?)

2. When you mention the “Ethernet Library,” are you referring to the IOlibrary provided by Wiznet?

It would be helpful if you could provide more details.

---

Source: https://maker.wiznet.io/forum/15730