Establishing SPI Communication between Arduino Uno and Nano: A Step-by-Step Guide

Introduction:

Serial Peripheral Interface (SPI) is a widely used communication protocol in embedded systems, particularly in microcontrollers like Arduino. SPI is a synchronous, full-duplex protocol that allows multiple devices to communicate with each other using a common set of pins.

In this setup, the SS (Slave Select) pin is used to select which device the master (Arduino Uno) wants to communicate with. The MOSI (Master Out Slave In) pin is used to send data from the master to the slave (Arduino Nano). The MISO (Master In Slave Out) pin is used to send data from the slave to the master. Finally, the SCK (Serial Clock) pin is used to synchronize the data transfer between the two devices.

Software Setup for SPI Communication between Arduino Uno and Nano:

To program the Arduino boards, we will use the Arduino IDE. First, we need to write the code for the master device (Arduino Uno).

//SPI MASTER (ARDUINO)
//SPI COMMUNICATION BETWEEN TWO ARDUINO 
//CIRCUIT DIGEST

#include<SPI.h>                             //Library for SPI 
#define LED 7           
#define ipbutton 2
int buttonvalue;
int x;
void setup (void)

{
  Serial.begin(115200);                   //Starts Serial Communication at Baud Rate 115200 
  
  pinMode(ipbutton,INPUT);                //Sets pin 2 as input 
  pinMode(LED,OUTPUT);                    //Sets pin 7 as Output
  
  SPI.begin();                            //Begins the SPI commnuication
  SPI.setClockDivider(SPI_CLOCK_DIV8);    //Sets clock for SPI communication at 8 (16/8=2Mhz)
  digitalWrite(SS,HIGH);                  // Setting SlaveSelect as HIGH (So master doesnt connnect with slave)
}

void loop(void)
{
  byte Mastersend,Mastereceive;          

  buttonvalue = digitalRead(ipbutton);   //Reads the status of the pin 2

  if(buttonvalue == HIGH)                //Logic for Setting x value (To be sent to slave) depending upon input from pin 2
  {
    x = 1;
  }
  else
  {
    x = 0;
  }
  
  digitalWrite(SS, LOW);                  //Starts communication with Slave connected to master
  
  Mastersend = x;                            
  Mastereceive=SPI.transfer(Mastersend); //Send the mastersend value to slave also receives value from slave
  
  if(Mastereceive == 1)                   //Logic for setting the LED output depending upon value received from slave
  {
    digitalWrite(LED,HIGH);              //Sets pin 7 HIGH
    Serial.println("Master LED ON");
  }
  else
  {
   digitalWrite(LED,LOW);               //Sets pin 7 LOW
   Serial.println("Master LED OFF");
  }
  delay(1000);
}

 

//SPI SLAVE (ARDUINO)
//SPI COMMUNICATION BETWEEN TWO ARDUINO 
//CIRCUIT DIGEST
//Pramoth.T

#include<SPI.h>
#define LEDpin 6
#define buttonpin 2
volatile boolean received;
volatile byte Slavereceived,Slavesend;
int buttonvalue;
int x;
void setup()

{
  Serial.begin(115200);
  
  pinMode(buttonpin,INPUT);               // Setting pin 2 as INPUT
  pinMode(LEDpin,OUTPUT);                 // Setting pin 7 as OUTPUT
  pinMode(MISO,OUTPUT);                   //Sets MISO as OUTPUT (Have to Send data to Master IN 

  SPCR |= _BV(SPE);                       //Turn on SPI in Slave Mode
  received = false;

  SPI.attachInterrupt();                  //Interuupt ON is set for SPI commnucation
  
}

ISR (SPI_STC_vect)                        //Inerrrput routine function 
{
  Slavereceived = SPDR;         // Value received from master if store in variable slavereceived
  received = true;                        //Sets received as True 
}

void loop()
{ if(received)                            //Logic to SET LED ON OR OFF depending upon the value recerived from master
   {
      if (Slavereceived==1) 
      {
        digitalWrite(LEDpin,HIGH);         //Sets pin 7 as HIGH LED ON
        Serial.println("Slave LED ON");
      }else
      {
        digitalWrite(LEDpin,LOW);          //Sets pin 7 as LOW LED OFF
        Serial.println("Slave LED OFF");
      }
      
      buttonvalue = digitalRead(buttonpin);  // Reads the status of the pin 2
      
      if (buttonvalue == HIGH)               //Logic to set the value of x to send to master
      {
        x=1;
        
      }else
      {
        x=0;
      }
      
  Slavesend=x;                             
  SPDR = Slavesend;                           //Sends the x value to master via SPDR 
  delay(1000);
}
}