---
title: "Connecting Modbus half duplex (A/B/Gnd) using WIZ750SR-485-EVB"
url: "https://maker.wiznet.io/forum/15983"
markdown_url: "https://maker.wiznet.io/forum/15983/md"
type: "Forum topic"
category: "Serial-to-Ethernet & ConfigTool"
author: "JohnWilliams"
created: "2026-01-30T05:36:10+09:00"
last_activity: "2026-01-30T14:19:47+09:00"
language: "en"
views: 5
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# Connecting Modbus half duplex (A/B/Gnd) using WIZ750SR-485-EVB

## Question

Asked by JohnWilliams on 2026-01-30 in Serial-to-Ethernet & ConfigTool.

How do I connect WIZ750SR-485-EVB board output to a Modbus RTU daisy chain?

I don't see an A/B plus Gnd connection (three wires). There are only TDX +/- and RXD +/- plus Gnd connections (five wires).

## Replies

### Reply 1 by TheoIm, 2026-01-30

Hi,

This board supports both RS-422 and RS-485, which is why the terminals are labeled as TX and RX.
However, in RS-485 (Modbus RTU) mode, RXD+ and RXD− function as the A/B differential pair.

For a Modbus RTU daisy-chain connection, simply connect:
**RXD+ → A**,
**RXD− → B**,
and **GND** as the common reference.

The TXD pins are intended for RS-422 (4-wire) operation and are not required for RS-485 2-wire communication.

Thank you

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Source: https://maker.wiznet.io/forum/15983