---
title: "W5100s and STM32 custom board SPI problem"
url: "https://maker.wiznet.io/forum/13632"
markdown_url: "https://maker.wiznet.io/forum/13632/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "jernejR"
created: "2020-01-05T17:57:24+09:00"
last_activity: "2020-03-02T02:01:56+09:00"
language: "en"
views: 776
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W5100s and STM32 custom board SPI problem

## Question

Asked by jernejR on 2020-01-05 in Ethernet Chips.

Hello,
I made custom board with W5100s and STM32. The STM32 part of the board works as expected but the W5100s part does not. When I tested SPI with oscilloscope MISO is low all the time.
I would like to ask you if you can see my schematics and help me find a error.

thank you very much

[![W5100S](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/a/a67013c08edb2ef3285bc7b6fe90486c973f8d8b.png) W5100S7102×4532 162 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/a/a67013c08edb2ef3285bc7b6fe90486c973f8d8b.png)

## Replies

### Reply 1 by Mon2, 2020-03-02

Hi. Not sure if you have this working but from a quick review of your posted schematic:

a) confirm you have applied the required filter caps for the voltage rails as noted in the datasheet

b) do not agree with the hard strapping of the #RST (RSTN) line to +3v3. Instead, consider to apply an external reset supervisor to meet the timing of low for xx time then high. In a pinch, a RC circuit should be ok but best to confirm with the Wiznet staff and/or check other application notes using this controller.

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Source: https://maker.wiznet.io/forum/13632