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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

...

Preparation

Take a look at the pinout

Image Added

Signal

Sub-D Pin

RS485-

1

RS485+

2

GND

5

+5V

6

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

Image Added

Signal

Pin

RS485-

D+

RS485+

D-

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

Image Added

Instructions for the Modbus-RTU Slave

  • Make the PiCtory configuration

  • Configure the RevPi Connect and the

...

  • Modbus RTU Slave

Image Modified

  • Configure the Modbus RTU Slave serial interface as follows

Image Modified

  • Save the configuration

Image Modified

  • Reset the driver

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Instructions for the Modbus-RTU Master

  • Open qModMaster

  • Configure the serial interface parameter

...

Image Added

...

  • Transfer 1,2,3 to the Registers

...

Image Added

...

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

Code Block
languagebash
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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