#define InterruptInputPin 2 // For checking if the input data is available
#define InterruptSensorPin 3 // For checking when to send data

#define IN0 A0
#define IN1 A1
#define IN2 A2
#define IN3 A3

#define OUT0 5
#define OUT1 6
#define OUT2 7
#define OUT3 8

volatile int ParallelInput; // The input data

//*************************************
void ReadParallel() //Reads input and saves it in parallelInput.
{
  if (digitalRead(IN0) == HIGH)
    bitWrite(ParallelInput,0,1);
    else
      bitWrite(ParallelInput,0,0);

  if (digitalRead(IN1) == HIGH)
    bitWrite(ParallelInput,1,1);
    else
      bitWrite(ParallelInput,1,0);

  if (digitalRead(IN2) == HIGH)
    bitWrite(ParallelInput,2,1);
    else
      bitWrite(ParallelInput,2,0);

  if (digitalRead(IN3) == HIGH)
    bitWrite(ParallelInput,3,1);
    else
      bitWrite(ParallelInput,3,0);

}
//***************************************

void WriteParallel() //Writes ParallelInput to output.
{
  detachInterrupt(digitalPinToInterrupt(InterruptInputPin));
  digitalWrite(OUT0,bitRead(ParallelInput,0));
  digitalWrite(OUT1,bitRead(ParallelInput,1));
  digitalWrite(OUT2,bitRead(ParallelInput,2));
  digitalWrite(OUT3,bitRead(ParallelInput,3));
  attachInterrupt(digitalPinToInterrupt(InterruptInputPin),ReadParallel,RISING);

}

void setup() {

  pinMode(IN0,INPUT);
  pinMode(IN1,INPUT);
  pinMode(IN2,INPUT);
  pinMode(IN3,INPUT);

  pinMode(OUT0,OUTPUT);
  pinMode(OUT1,OUTPUT);
  pinMode(OUT2,OUTPUT);
  pinMode(OUT3,OUTPUT);
  attachInterrupt(digitalPinToInterrupt(InterruptInputPin),ReadParallel,RISING);


attachInterrupt(digitalPinToInterrupt(InterruptSensorPin),WriteParallel,RISING);

}

void loop() {

}