#include <SPI.h>

// * CS - to digital pin 10  (SS pin)
// * SDI - to digital pin 11 (MOSI pin)
// * SDI - to digital pin 12 (MISO pin)
// * CLK - to digital pin 13 (SCK pin)

// Vorbereitungen um als Slave Daten zu empfangen
char recieve_buff [100];
volatile byte pos;
volatile boolean process_it;

// PINS fuer SPI
const int slaveSelectPin = 10;
const int miso = 12;
const int mosi = 11;

const int ledPin = 2;


void setup() {   

  pinMode(slaveSelectPin, INPUT); 
  pinMode(miso, OUTPUT);

  // SPI als Slave aktivieren
  SPCR |= _BV(SPE);

  // interrupt vorbereitung
  pos =0; //recieve Buffer leer
  process_it = false;
  SPI.attachInterrupt();

  // initialize the digital pin as an output.
  pinMode(ledPin, OUTPUT);

  digitalWrite (ledPin, HIGH);
  delay(1000);
  digitalWrite (ledPin, LOW);
}

//PINS/Bitmask fuer LEDs
int LED0 = 0x01;
int LED1 = 0x02;
int LED2 = 0x04;
int LED3 = 0x08;

int PWM_BASE = 15;


ISR (SPI_STC_vect)
{
  byte c = SPDR; 
  if (pos < sizeof recieve_buff)
  {
    recieve_buff[pos++] = c;
    process_it = true;
  }
}


void loop()
{

  //Verarbeitung der empfangenen Nachricht
  if (process_it == true)
  { 
    if (recieve_buff[pos] == 0x31)
      digitalWrite (ledPin, HIGH);
    else if (recieve_buff[pos] == 0x30)
      digitalWrite (ledPin, LOW);
      
    process_it == false;
    pos = 0;
  }
}