#define SW1 3
#define LED 13

volatile int8_t SW1State;

void setup() {
  
  pinMode(SW1, INPUT);
  pinMode(LED, OUTPUT);
  
  attachInterrupt(digitalPinToInterrupt(SW1), SW1StateUpdate, CHANGE);
 
  SW1State = digitalRead(SW1);
  
}

void loop() {
  
  //int8_t SW1State = digitalRead(SW1);
  //digitalWrite(LED, SW1State);
  delay(1000);
  
}

void SW1StateUpdate() {
  
  SW1State = !SW1State;
  digitalWrite(LED, SW1State);
  
}