---
title: "Control of PHYCFGR/OPMDC for adapter mode control"
url: "https://maker.wiznet.io/forum/14258"
markdown_url: "https://maker.wiznet.io/forum/14258/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "Stimpy"
created: "2021-06-09T23:13:21+09:00"
last_activity: "2021-06-21T22:03:45+09:00"
language: "en"
views: 474
replies: 2
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# Control of PHYCFGR/OPMDC for adapter mode control

## Question

Asked by Stimpy on 2021-06-09 in Ethernet Chips.

Hi;
From the spec sheet I can see that iis possible to set the operation of the adapter (i.e. 10MB half Duplex) by setting the PHYCFGR register. Does the ARD lib have this ability?
Stimpy

## Replies

### Reply 1 by irina, 2021-06-14

W5500 is connected to MDC/MDIO pin of PHY, MDC/MDIO pin are read/write signals the register of PHY.
If you want to control the PHY data of W5500, please refer the source code of W5500 EVB.

![](https://avatars.discourse-cdn.com/v4/letter/s/779978/48.png) Stimpy:

> Does the ARD lib have this ability?

I can’t answer your question because I don’t understand the question.

### Reply 2 by Stimpy, 2021-06-21 (in reply to reply 1)

Hi Ms. Kim;
I am trying to get the W5500 to use the 10 MB simplex mode to link with another net appliance that requires this configuration. I am using the ethernet 2.0.0.0 lib for Arduino which I have had to modify to get this adapter control to work. So far I have been able to use some code that uses the register know as PHYCFGR to set that to XX000XXX so the OPMDC bits look correct . In other words if I set and get the PHYCFGR register it looks correct for the bits that control the adapter mode. 0 0 0 is supposed to be the setting for 10 MB simplex. But the second bit (bit 1 marked as the RO speed indicator bit) in the set reads back as a 1. So even though I set the W5500 to use 10 MB speed, it is still set for 100 MB. Why?
Also the other device never links with the W5500. It will do with an adapter in a PC set for 10 MB simplex.
Thanks for your time
Stimpy

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Source: https://maker.wiznet.io/forum/14258