Example Program Arduino Modbus RTU Slave

The following is an example of an Arduino modbus RTU Slave program for Read Digital Input, Write Digital Output, Read Analog Input, Write Analog Output. For modbys library, please download HERE

OK, here's the code

#include <modbus.h>
#include <modbusDevice.h>
#include <modbusRegBank.h>
#include <modbusSlave.h>

/* PINS
Add more registers if needed
Digital input pins 2,3,4,5,6,7
Digital output pins 8,9,12,13
Analog output pins 10,11 (PWM)
Analog input pins 0,1,2,3,4,5
*/


modbusDevice regBank;
modbusSlave slave;

int AI0,AI1,AI2,AI3,AI4,AI5;


void setup()
{   
  regBank.setId(1); ///Set Slave ID

//Add Digital Input registers
  regBank.add(10002);
  regBank.add(10003);
  regBank.add(10004);
  regBank.add(10005);
  regBank.add(10006);
  regBank.add(10007);
// Add Digital Output registers
  regBank.add(8);
  regBank.add(9);
  regBank.add(12);
  regBank.add(13);
//Analog input registers
  regBank.add(30001);
  regBank.add(30002);
  regBank.add(30003);
  regBank.add(30004);
  regBank.add(30005);
  regBank.add(30006);
//Analog Output registers
  regBank.add(40010); 
  regBank.add(40011); 

  slave._device = &regBank; 
  slave.setBaud(9600);   
 
  pinMode(2,INPUT);
  pinMode(3,INPUT);
  pinMode(4,INPUT);
  pinMode(5,INPUT);
  pinMode(6,INPUT);
  pinMode(7,INPUT);
  pinMode(8,OUTPUT);
  pinMode(9,OUTPUT);
  pinMode(12,OUTPUT);
  pinMode(13,OUTPUT);
   
}
void loop(){

  while(1){   
  //Digital Input
    byte DI2 = digitalRead(2);
    if (DI2 >= 1)regBank.set(10002,1);
    if (DI2 <= 0)regBank.set(10002,0);
    byte DI3 = digitalRead(3);
    if (DI3 >= 1)regBank.set(10003,1);
    if (DI3 <= 0)regBank.set(10003,0);
    byte DI4 = digitalRead(4);
    if (DI4 >= 1)regBank.set(10004,1);
    if (DI4 <= 0)regBank.set(10004,0);
    byte DI5 = digitalRead(5);
    if (DI5 >= 1)regBank.set(10005,1);
    if (DI5 <= 0)regBank.set(10005,0);
    byte DI6 = digitalRead(6);
    if (DI6 >= 1)regBank.set(10006,1);
    if (DI6 <= 0)regBank.set(10006,0);
    byte DI7 = digitalRead(7);
    if (DI7 >= 1)regBank.set(10007,1);
    if (DI7 <= 0)regBank.set(10007,0);
                               
  //Digital output
    int DO8 = regBank.get(8);
      if (DO8 <= 0 && digitalRead(8) == HIGH)digitalWrite(8,LOW);
      if (DO8 >= 1 && digitalRead(8) == LOW)digitalWrite(8,HIGH);
   
    int DO9 = regBank.get(9);
      if (DO9 <= 0 && digitalRead(9) == HIGH)digitalWrite(9,LOW);
      if (DO9 >= 1 && digitalRead(9) == LOW)digitalWrite(9,HIGH);
    int DO12 = regBank.get(12);
      if (DO12 <= 0 && digitalRead(12) == HIGH)digitalWrite(12,LOW);
      if (DO12 >= 1 && digitalRead(12) == LOW)digitalWrite(12,HIGH);
    int DO13 = regBank.get(13);
      if (DO13 <= 0 && digitalRead(13) == HIGH)digitalWrite(13,LOW);
      if (DO13 >= 1 && digitalRead(13) == LOW)digitalWrite(13,HIGH);
           
  //Analog input  ***READ Twice deliberately
    AI0 = analogRead(0);
    delay(5);
    AI0 = analogRead(0);
    regBank.set(30001, (word) A0);
    delay(10);
   
    AI1 = analogRead(1);
    delay(5);
    AI1 = analogRead(1);
    regBank.set(30002, (word) AI1);
    delay(10);
   
    AI2 = analogRead(2);
    delay(5);
    AI2 = analogRead(2);
    regBank.set(30003, (word) AI2);
    delay(10);
   
    AI3 = analogRead(3);
    delay(5);
    AI3 = analogRead(3);
    regBank.set(30004, (word) AI3);
    delay(10);
   
    AI4 = analogRead(4);
    delay(5);
    AI4 = analogRead(4);
    regBank.set(30005, (word) AI4);
    delay(10);
   
    AI5 = analogRead(5);
    delay(5);
    AI5 = analogRead(5);
    regBank.set(30006, (word) AI5);
    delay(10);
       
  //Analog output
    word AO10 = regBank.get(40010);
    analogWrite(10,AO10);
    delay(10);
    word AO11 = regBank.get(40011);
    analogWrite(11,AO11);
    delay(10);
       
  slave.run(); 
  }
}

Upload the code to Arduino.

Next for the test .. we will use the qModmaster application

Modbus RTU configuration settings as shown above, for Serial Port, please adjust it to the serial port that you are using.

and here I will read the Analog input register data with addresses 30001, and 30002

here it can be seen that the data values of the registers 3001 = 1023, and 30002 = 952.

Okay that's it for now & good luck