---
title: "W5500 always send RST in TCP handshake"
url: "https://maker.wiznet.io/forum/10452"
markdown_url: "https://maker.wiznet.io/forum/10452/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "kw123"
created: "2014-08-18T07:17:50+09:00"
last_activity: "2017-05-04T08:33:38+09:00"
language: "en"
views: 709
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W5500 always send RST in TCP handshake

## Question

Asked by kw123 on 2014-08-18 in Ethernet Chips.

Dears,
I’ve got a wiz55io module.It work fine with PING.

```
I write a Modbus TCP server program from Freemodbus.But it can't work.I capture the data to analyze this problem.I found the W5500 always send back RST in TCP handshake.
Then I download a TCP_loopback program from website.It still work fine with PING,but still send back RST in TCP handshake.
I don't know what wrong with it,please give me some advise! Thank you all.
```

[STM32_W5500_Modbus_TCP_V1.zip](https://maker.wiznet.io/forum/legacyFile.asp?path=1viHEqCpv2tE1hLMOhMCNMw14xQ.zip) (376 KB)
[handshake error.rar](https://maker.wiznet.io/uploads/short-url/4bhX80wAlvvFdPDtq4So3mc1x3a) (187 KB)

[![](https://maker.wiznet.io/forum_uploads/wiznet/original/1X/a918e7d4ebd1c5fe266b5af214e0242fd19193fd.jpg) 1279×270 220 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/1X/a918e7d4ebd1c5fe266b5af214e0242fd19193fd.jpg)

## Replies

### Reply 1 by kw123, 2014-08-18

I’ve already know what’s the problem is.
TCP initialize error.I’m doing with it.

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Source: https://maker.wiznet.io/forum/10452