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This tutorial shows how to do a Modbus RTU communication with the RevPi Connect and a USB-RS485 converter.

Here we are using QModMaster as Modbus Master and the RevPi Connects RS485 interface.

So the PC acts as the Modbus Master and the RevPi Connect acts as the Modbus Slave.

You need the following

A USB-RS485 Converter
The software qModMaster

Take a look at the pinout

Here is an example product, the DIGITUS USB to serial adapter

Some USB-Serial adaptors have just the two data signal lines, i.e. the USB-RS485 Converter from our shop

Preparation

Take a look at the tutorial “How to Connect Serial Devices”
- Connect the RS485+ signal line
- Connect the RS485- signal line
- Optionally connect the GND pin

Instructions for the Modbus-RTU Slave

Instructions for the Modbus-RTU Master

Read it out on the RevPi Connect shell using the “piTest” command

Code Block

language	bash

pi@RevPi14607:~ $ piTest -1 -r Input_1
2 Byte-Value of Input_1: 1 dez (=0001 hex)
pi@RevPi14607:~ $ piTest -1 -r Input_2
2 Byte-Value of Input_2: 2 dez (=0002 hex)
pi@RevPi14607:~ $ piTest -1 -r Input_3
2 Byte-Value of Input_3: 3 dez (=0003 hex)

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Verwandte Vorgänge

Signal	Pin
RS485-	D+
RS485+	D-

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