#include "SPI.h"
#define LED 13           
#define ipbutton 2
 
int buttonvalue;
int x;
 
void setup () {  
  pinMode(ipbutton, INPUT);
  pinMode(LED, OUTPUT);
  
  SPI.begin();
  SPI.setClockDivider(SPI_CLOCK_DIV8);
  digitalWrite(SS, HIGH);
}
 
void loop() {
  byte Mastersend, Mastereceive;          
  buttonvalue = digitalRead(ipbutton);
  if(buttonvalue == HIGH) { x = 1; }
  else { x = 0; }
  
  digitalWrite(SS, LOW); 
  Mastersend = x;                            
  Mastereceive = SPI.transfer(Mastersend);
  
  if(Mastereceive == 1) { digitalWrite(LED, HIGH); }
  else { digitalWrite(LED, LOW); }
  delay(100);
}



Скетч для ведомой платы SPI Arduino Uno (slave)
#include "SPI.h"
#define LEDpin 13
#define buttonpin 2
 
volatile boolean received;
volatile byte Slavereceived,Slavesend;
int buttonvalue;
int x;
 
void setup() { 
  pinMode(buttonpin, INPUT);
  pinMode(LEDpin, OUTPUT);
  pinMode(MISO, OUTPUT);
  SPCR |= _BV(SPE);
  received = false;
  SPI.attachInterrupt();
}
 
ISR (SPI_STC_vect) {
  Slavereceived = SPDR;
  received = true;
}
 
void loop() {
  if(received) {
    if (Slavereceived==1) { digitalWrite(LEDpin, HIGH); }
    else { digitalWrite(LEDpin, LOW); }
      
    buttonvalue = digitalRead(buttonpin);
    if (buttonvalue == HIGH) { x=1; }
    else { x=0; }
      
    Slavesend=x;                             
    SPDR = Slavesend; 
    delay(100);
  }
}