---
title: "W6100 read/write MAC"
url: "https://maker.wiznet.io/forum/14396"
markdown_url: "https://maker.wiznet.io/forum/14396/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "sergyv"
created: "2021-11-10T11:53:49+09:00"
last_activity: "2022-08-23T09:52:30+09:00"
language: "en"
views: 479
replies: 3
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W6100 read/write MAC

## Question

Asked by sergyv on 2021-11-10 in Ethernet Chips.

Hello!

When on startup I try to write MAC address I use the following SPI command:

41 20 04 01 02 03 04 05 06

And I get response:
01 02 03 00 00 00 00 00 00

But then I try to read it with:
41 20 00 00 00 00 00 00 00
And get the reply:
01 02 03 00 00 00 00 00 00

My SPI comms work as I get 01 02 03 at the start. But why the register is empty?

## Replies

### Reply 1 by louis, 2021-11-12

Hello

There’s no address inside the chip.
You have to buy it separately and add address.

Thank you

### Reply 2 by Himmat, 2022-05-27

Hello louis,
I am facing same type of problem in my project where I am using valid MAC value “0x0013E1170001”.
Steps are:
41 20 04 00 13 E1 17 00 01

And I get response:
01 02 03 00 00 00 00 00 00

But then I try to read it with:
41 20 00 00 00 00 00 00 00
And get the reply:
01 02 03 00 00 00 00 00 00

Please let me know what can be the issue?

Thanks,
Himmat

### Reply 3 by Welocs, 2022-08-23

Hi,

your SPI stream is correct. You address 0x4120 (first byte of SHAR), Bank 0 (common registers) and you try writing variable length (0x04) and then reading variable length (0x00).

I had issues with my breadbord wirings, where i thought, it was software (read my thread about this). Try reading the CIDR and VER registers to verify your SPI is working properly.

What is your SPI speed?

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Source: https://maker.wiznet.io/forum/14396