---
title: "W5500 - TX_WR pointer math"
url: "https://maker.wiznet.io/forum/13889"
markdown_url: "https://maker.wiznet.io/forum/13889/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "Dan1"
created: "2020-06-14T12:04:31+09:00"
last_activity: "2020-06-18T07:40:35+09:00"
language: "en"
views: 508
replies: 3
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W5500 - TX_WR pointer math

## Question

Asked by Dan1 on 2020-06-14 in Ethernet Chips.

Hello all:
I would like to understand the way W5500 handles TX_WR pointer.
I read the pointer twice:
Once at *wiz_send_data()* routine and once after *send()* rutine;
I expect that when reading it at the second time it will be larger by the *len* value, added to it before executing the *send* command.
I found that when it becomes larger than 0xFF it always shows the upper byte as 0x00!!
Example:
len = 0x9C
TX_WR = 0x0091 //before send()
TX_WR =0x002D //second reading-expecting it to be ***0x012D***

Why TX_WR is not ***0x012D*** after send()? (it is 16 bits pointer…)
Might be printf() problem…
Any idea?
Thanks
Dan

## Replies

### Reply 1 by bangbh, 2020-06-17

Hello
I tested like the picture below.
![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/8/8151aeae65d49a3b89e3ad1047b7a05508fababd.png)
![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/e/eb1131ec7760b134cfee2365093e382837a1f540.png)

I don’t know exactly how many bytes I sent, but I seems work fine.

Thanks.

### Reply 2 by Dan1, 2020-06-17 (in reply to reply 1)

Hi, Thanks for responding.
I Am sure that it work alright. I guess it is monitoring issue but yet I have problem of a lot of extra bytes received by the server when I send a string to it.
I have to find the reason to that phenomena in order to be able to feed server with the
data collected by my sensors.
Any idea?
Regards
Dan

### Reply 3 by Dan1, 2020-06-18 (in reply to reply 1)

OK, I got every thing OK now. re compiled with last version of ioLibraray…
Thanks

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Source: https://maker.wiznet.io/forum/13889