Communication Modbus Arduino as Slave

posted in: Microcontroller, PLC | 1

Modbus is an industrial communication protocol standard that operates on the principle of “Master – Slave”. One Master can connect to many Slaves. Currently, most industrial devices use Modbus, so in order for the arduino to communicate with PLCs, HMIs, inverters, etc. betfinal بالعربي , we must be able to put the Modbus protocol into Arduino. You should read the articles about Modbus first to understand more before programming.

Today’s content is:

“Use Modbus RS485 to communicate between arduino and Modbus Poll”

  1. Prepare
  • Modbus Poll software , Modbus Poll is a Modbus master emulator mainly designed to help Modbus device developers or others who want to test and simulate the Modbus protocol. 
  • UART TTL to RS485 communication converter circuit (This circuit to convert UART to RS485 output of the circuit you can connect to the communication port of other Modbus devices).
  • USB to RS485 Converter (This circuit helps to connect RS485 to the computer’s USB port)
  • ModbusRtu Library for Arduino

2. Wiring diagram

3. Programming

Here I use register au16data[0] to switch off Led pin 12 and register au16data[12] to store analog value of pin A0.

#include <ModbusRtu.h>

// data array for modbus network sharing
uint16_t au16data[16] = {
  0, 1415, 9265, 4, 2, 7182, 28182, 8, 0, 0, 0, 0, 0, 0, 1, -1 };

 *  Modbus object declaration
 *  u8id : node id = 0 for master, = 1..247 for slave
 *  port : serial port
 *  u8txenpin : 0 for RS-232 and USB-FTDI 
 *               or any pin number > 1 for RS-485
Modbus slave(1,Serial,2); // this is slave @1 and RS-485 chân 2

void setup() {
  Serial.begin(9600,SERIAL_8E1); // baud-rate at 9600

void loop() {
  slave.poll( au16data, 16 );
  if (au16data[0]==1) digitalWrite(12,HIGH);
  else digitalWrite(12,LOW);
  au16data[12] = analogRead(A0);

4. Connect Modbus Poll to Arduino

Go to Connection > Connect install as follows

Where 9600 is the Baud rate and Even Parity is the error checking mode corresponding to the command line Serial.begin(9600,SERIAL_8E1);

After connecting, go to Setup > Read/ Write Definition.

Slave ID above I set to 1, you can change other values ​​in the code, choose Function 03 (Read the document to understand more about Modbus), The address is 0 and the number is 16 registers. لعبة الكازينو


To turn on the LED on pin 12, double-click on the 0 register and change the Value to 1.

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