#include <SPI.h>

static boolean received = false;

static byte message;

ISR (SPI_STC_vect)
{
  message = SPDR;                  
  received = true;                       
}

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(MISO,OUTPUT);
  SPCR |= (1<<SPE);  
  SPI.attachInterrupt(); 
}

void loop() {
  // put your main code here, to run repeatedly:
  if (received) {
   Serial.print("message received: 0x");
   Serial.println(message, HEX);
  }
}