const int ledPin = PA5;     
const int buttonPin = PA0;  

volatile bool led_state = false;

void Button_ISR() 
{
    led_state = !led_state;
    digitalWrite(ledPin, led_state); 
}

void setup() 
{
    pinMode(ledPin, OUTPUT);
    
    pinMode(buttonPin, INPUT_PULLUP);
    
    attachInterrupt(digitalPinToInterrupt(buttonPin), Button_ISR, FALLING);
}

void loop() 
{
    delay(100); 
}