// the number of the pushbutton pin
const int buttonPin = PB0;
// the number of the LED pin
const int ledPin =  PB1;

int ledState = 0;
int buttonState = 0;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT);
}

void loop() {
  // Read the button
  int btn = digitalRead(buttonPin);
  // when button state has changed and is pressed
  if (btn != buttonState && btn == HIGH) {
    // toggle the logical LED state
    if (ledState == HIGH) {
      ledState = LOW;
    } else {
      ledState = HIGH;
    }
    // and make the logical real
    digitalWrite(ledPin, ledState);
  }
  buttonState = btn;
}