---
title: "W5500 returning data byte zero always"
url: "https://maker.wiznet.io/forum/14143"
markdown_url: "https://maker.wiznet.io/forum/14143/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "Elie Assaf"
created: "2021-02-05T09:14:48+09:00"
last_activity: "2021-02-25T07:53:27+09:00"
language: "en"
views: 841
replies: 7
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W5500 returning data byte zero always

## Question

Asked by Elie Assaf on 2021-02-05 in Ethernet Chips.

Hello

I am using the W5500 chip. But whenever I try to read (and I think also it’s happening with write), I get the “010203” bytes, but I always get the data byte as 0. Even though both MOSI and MISO are toggled at the falling edge of the CLK. Does anyone know why this might be happening?

The following is the scope of one SPI transfer, with OM=1 (FDM, 1Byte)

Reading the VERSIONR:

[![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/2/2c9ac189cf91624622fc2c46c2a5ce064cb8965e.png) image1614×274 25 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/2/2c9ac189cf91624622fc2c46c2a5ce064cb8965e.png)

## Replies

### Reply 1 by irina, 2021-02-07

I think you are doing a write operation, not a read operation.

[![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/d/d05cb14f5231835240b5ed7fec5f6022b20c35e6.png) image695×196 15.6 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/d/d05cb14f5231835240b5ed7fec5f6022b20c35e6.png)

![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/4/49811a069934bf747a31cc7c869c7faffa33c715.png)

If you only want to read 1byte of version register, this value is 00 39 0**0** 00.
Change the value and try again.

### Reply 2 by Elie Assaf, 2021-02-08 (in reply to reply 1)

Hello Kim

Thanks for your reply.

In fact, this 01 byte corresponds to the Control byte, for which the 2 LSBs are the OM(VDM or FDM), and not the R/W bit. Anyway, I tried to do it with VDM (OM=0), and got the same result:

[![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/5/5916132646e8e4a7da149a28f6d8e035af55bdf4.png) image1631×309 27.3 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/5/5916132646e8e4a7da149a28f6d8e035af55bdf4.png)

### Reply 3 by Elie Assaf, 2021-02-10

I still don’t have any interpretation.
I tried all R/Ws on all registers, FDM and VDM, and I never have any data. I’m not sure the chip is interpreting well my control.
Anyway, I noticed now that on the MISO line, at the end of a test, I see some flipping, that is not continuous, of a frequency of 25MHz, before the line settles from 0 to 1.

Also, in VDM, I’m seeing that the chip resends the 010203 bytes on MISO after each 4 data bytes. Does this signify
anything?

These screenshots show the toggling at the end of a test

[![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/9/918c12670cffac8616612f93ecae2b8277c0eb1b.png) image1585×277 23.8 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/9/918c12670cffac8616612f93ecae2b8277c0eb1b.png)

[![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/111dce28a63d0804194b3b10d7d3dcdb323a286b.png) image1674×261 23.5 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/1/111dce28a63d0804194b3b10d7d3dcdb323a286b.png)

### Reply 4 by irina, 2021-02-22

The value mean a per-phase byte numbering and does not affect the system.

01 : Address phase(high -Address )
02 :Address phase( low - address)
03 : control phase
Isn’t the MISO line connected elsewhere?
It’s also hard for me to figure out what the cause…
I will try to fine the cause,too

### Reply 5 by Elie Assaf, 2021-02-22

I see, we suggested what you said.
I don’t know about the MISO, the W5500 is implemented on a board with other components.
We suggested it might be a clock issue, maybe caused by the external 25MHz clock, affecting the registers.
I stopped working on W5500 now and bought a W6100 and started working on it.
Thank you.

### Reply 6 by irina, 2021-02-25

Does the same problem appear on the W6100?

### Reply 7 by Elie Assaf, 2021-02-25

No. W6100 is working perfectly, except that I can’t write on the MSSR, that’s the only register that’s unwritable, and I still don’t know why.

If you have any idea it would be great:

[W6100 MSSR unwritable](https://forum.wiznet.io/t/topic/8462/) [W6100](https://maker.wiznet.io/c/tcp-ip-chip/w6100/155)

> 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?

Thanks.

---

Source: https://maker.wiznet.io/forum/14143