#include <avr/io.h>
#include <avr/interrupt.h>


volatile data;

int main (void)
{
	DDRD |= (1<<PD0);
	PORTD |= 0x00;

    DDRB &= ~((1<<2)|(1<<3)|(1<<5));   // SCK, MOSI and SS as inputs
    DDRB |= (1<<4);                    // MISO as output

    SPCR &= ~(1<<MSTR);                // Set as slave
    SPCR |= (1<<SPR0)|(1<<SPR1);       // divide clock by 128
    SPCR |= (1<<SPIE);                 // Enable SPI Interrupt
    SPCR |= (1<<SPE);                  // Enable SPI

    sei();

    while(1)
    {

    }
}

ISR (SPI_STC_vect)
{
    data = SPDR;
    PORTD ^= (1<<PD0);

}




#include <avr/io.h>
#include <avr/interrupt.h>

volatile data;

int main (void)
{
    char blah;

    DDRB |= (1<<2)|(1<<3)|(1<<5);    // SCK, MOSI and SS as outputs
    DDRB &= ~(1<<4);                 // MISO as input

    SPCR |= (1<<MSTR);               // Set as Master
    SPCR |= (1<<SPR0)|(1<<SPR1);     // divided clock by 128
    SPCR |= (1<<SPIE);               // Enable SPI Interrupt
    SPCR |= (1<<SPE);                // Enable SPI


    sei();

    while(1)
    {
        if ((SPSR & (1<<SPIF)) > 0)  // checks to see if the SPI bit is clear
            data=blah;               // send the data


    }
}


ISR (SPI_STC_vect)
{
    SPDR = data;
}