---
title: "W6100 MSSR unwritable"
url: "https://maker.wiznet.io/forum/14161"
markdown_url: "https://maker.wiznet.io/forum/14161/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "Elie Assaf"
created: "2021-02-17T14:41:22+09:00"
last_activity: "2021-02-18T09:52:36+09:00"
language: "en"
views: 499
replies: 2
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W6100 MSSR unwritable

## Question

Asked by Elie Assaf on 2021-02-17 in Ethernet Chips.

Hello

I’m trying to write on the S0_MSSR, but it’s not changing, it’s always 0x00.
I’m writing before the S0_CR_OPEN command, as required by the DS.
Anyone knows why?

## Replies

### Reply 1 by becky, 2021-02-18

![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/199a69b456fe5589f6ba034fde8104e54f0a36cf.png)

I doubt your interface is working. Please check the read-only registers such as version. Or, check the register address again.
Because in the case of S0_MSSR, the value is not set to 0.

### Reply 2 by Elie Assaf, 2021-02-18 (in reply to reply 1)

In the table, it’s said that the Reset value is 0x00, and in the description it’s said it’s 0xFF.
I’m reading and writing successfully on other registers, testing MACRAW. It’s working.

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Source: https://maker.wiznet.io/forum/14161