boolean pinState;

int8_t interruptPin = 19;
volatile int8_t pinStateChanged = false;

void setup()
{

  pinMode(interruptPin, INPUT);
  attachInterrupt(digitalPinToInterrupt(interruptPin), on_change_state, CHANGE);

  Serial.begin(115200);

  Serial.print(F("Pin "));
  Serial.print(interruptPin);
  Serial.print(F(" have interrupt "));
  Serial.println(digitalPinToInterrupt(interruptPin));

  interrupts();

}

void loop()
{

  if (pinStateChanged)
  {
    pinStateChanged = false;


    Serial.println();

    Serial.print(F("Arduino pin: "));
    Serial.print(interruptPin);
    Serial.write(': ');

    pinState = digitalRead(interruptPin);

    if (pinState)
      Serial.print(F("HIGH "));
    else
      Serial.print(F("LOW  "));

    Serial.println(digitalRead(interruptPin), BIN);

    Serial.print(F("Atmega 2560 pin for it is 45, PD2:"));

    // For Arduino Mega 2560 and pin 19, related chip pin is PD2.

    // Following should generate the same machine code
    // pinState = PIND & (1 << PD2);
    pinState = bitRead(PIND, PD2);

    if (pinState)
      Serial.print(F("HIGH "));
    else
      Serial.print(F("LOW  "));

    Serial.println(PORTD, BIN);

  }
};

void on_change_state() {

  pinStateChanged = true;

}