---
title: "W550 16-bit register read safety"
url: "https://maker.wiznet.io/forum/11188"
markdown_url: "https://maker.wiznet.io/forum/11188/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "danq"
created: "2015-07-19T14:01:02+09:00"
last_activity: "2017-05-04T08:36:25+09:00"
language: "en"
views: 491
replies: 0
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W550 16-bit register read safety

## Question

Asked by danq on 2015-07-19 in Ethernet Chips.

The W5500 manual specifies that some of the 16-bit registers may have their values changed in the middle of a read operation. In particular, the following registers: Sn_TX_FSR , Sn_RX_RSR. It is recommended that they be read multiple times and compared until two successive reads yield the same value.

Other 16-bit registers, such as : Sn_RX_RD , Sn_RX_WR and other address registers do not have this restriction noted in the user manual.

Can anyone confirm if it is safe to do a single read of these other registers or do they too have to have multiple read-and-compare in order to ensure a correct 16-bit read?

Also, perhaps I have an outdated user manual. Is the read restriction still valid on the Sn_TX_FSR and Sn_RX-RSR registers?

Cheers!

Daniel

---

Source: https://maker.wiznet.io/forum/11188