Modbus RTU Communication
- Dirk Conzelmann
- Ulrich Kouatang Biakoup
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
The software qModMaster
Take a look at the pinout
Here is an example product, the DIGITUS USB to serial adapter
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
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
Make the PiCtory configuration
Configure the RevPi Connect and the Modbus RTU 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)