Arduino SPI-to-Serial Slave

arduino-evt-spi-testing.ino

/*
 * A short Arduino sketch which waits for a SPI character to be sent from a
 * master device and then prints the received character over Serial.
 */

#include "Arduino.h"
#include <avr/io.h>

void setup()
{
   Serial.begin(115200);
   SPCR |= (1 << SPE);  // enable the SPI peripheral
}


void loop()
{
   if (SPSR & (1 << SPIF))
   {
      // if a SPI message has been received, print it
      Serial.println(SPDR, HEX);
   }
}