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Modbus-RTU Communication

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This tutorial shows how to do a Modbus-RTU communication with the RevPi Connect and an 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

Have a look at the pinout

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

Signal

Pin

RS485-

D+

RS485+

D-

Preparation

Instructions for the Modbus-RTU Slave

  • Make the PiCtory configuration

  • Configure the RevPi Connect and the ModbusRTU Slave

  • Configure the Modbus RTU Slave serial interface as follows

  • Save the configuration

  • Reset the driver

Instructions for the Modbus-RTU Master

  • Open qModMaster

  • Configure the serial interface parameter

  • Transfer 1,2,3 to the Registers

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

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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