Nucleo blink

// Blink: the smallest thing a board can do.
//
// The Nucleo's green LED LD2 hangs off D13, which is the STM32's PA5, through
// a resistor to ground, so HIGH lights it, as on an Uno. LED_BUILTIN, 13, D13
// and PA5 all name the same pin here.
//
// delay() parks the core on WFI between SysTick ticks rather than spinning, so
// this sketch costs the simulator almost nothing while it waits.

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);  // lit
  delay(500);
  digitalWrite(LED_BUILTIN, LOW);   // dark
  delay(500);
}